Migrando aplicações do Internet Explorer para o Mozilla

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Introdução

Depois que o Netscape inicializa o navegador Mozilla, ele faz requisição para o suporte dos padrões do W3C. Como resultado, o Mozilla não é completamente compativel com o navegador Netscape 4.x e as "heranças" dos códigos do Internet Explorer; por exemplo, o Mozilla não possui suporte a <layer> como eu discutirei mais adiante. Navegadores, como o Internet Explorer 4, que foram construidos antes da concepção dos padrões W3C herdaram algumas características.

Neste artigo, eu irei descrever as circunstâncias destas características no Mozilla, o qual, providencia um HTML robusto e compativel com o IE e outros navegadores.

Eu irei também falar sobre tecnologias não padronizadas, assim como XMLHttpRequest e edição de rich text, que o Mozilla suporta devido a não existir algo equivalencia ao W3C. Incluindo :

Mesmo que os padrões Web existam, diferentes browsers comportam de maneira também diferente ( é fato que os browsers podem comportar-se diferentemente dependendo da plataforma ). Muitos browsers, assim como o IE, também suporta pre-W3C APIs e não tem um suporte aprofundado para as unidades compativeis com W3C.

Antes que eu vá a fundo nas diferencas entre Mozilla e o IE, irei falar alguns modos básicos para você poder criar uma aplicação Web flexivel para mudanças de browser no futuro.

Visto que diferentes browsers alguns browsers algumas vezes usam diferentes APIs para alguma funcionalidade, você pode frequentemente usar multiplos blocos if() else() por todo o código para se diferenciaar entre os browsers. O seguinte bloco de código mostra uma designinação para o IE:

. . . 

var elm; 

if (ns4)
  elm = document.layers["myID"]; 
else if (ie4) 
  elm = document.all["myID"]

O código acima não está extensível, portanto, se você deseja ter suporte a um novo browser, você prescisa ajustar este bloco para toda a sua aplicação Web.

O meio mais fácil para eliminar a necessidade de reescrever o código para se ajustar a um novo browser está em uma funcionalidade abstrata. Preferencialmente que múltiplos blocos if() else(), você incrementou eficientemente com tarefes comuns e simplificando com suas proprias funções externas. Isto não apenas facilita para ler o código, isto simplifica a adição de novos clientes :

var elm = getElmById("myID"); 

function getElmById(aID){ 
  var element = null; 

  if (isMozilla || isIE5) 
    element = document.getElementById(aID);
  else if (isNetscape4) 
    element = document.layers[aID];
  else if (isIE4) 
    element = document.all[aID];

  return element; 
} 

O código acima usa o esquema chamado browser sniffing, ou detecção de qual browser o usuário está usando. Browser sniffing é comumente usado com o auxilio do Useragente, assim como :

Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.5) Gecko/20031016 

Quanto usamos o useragente para determinar o browser, ele nos retorna informações detalhadas sobre o browser em uso, códigos que os esquemas de reconhecimento dos useragents frequentemente podem cometer erros com novos browsers não implementados no código, isto requer algumas alterações no código.

Se o tipo do browser não têm importância (supondo que você já tem bloqueado os browsers não suportados para o acesso da aplicação Web), é melhor e mais confiável fazer uma detecção por capacidade do browser ou por características dos Objetos. Você pode freqüentemente fazer isto por meio testes de funcionalidade usando JavaScript. Por exemplo, assim como:

if (isMozilla || isIE5) 

Você pode usar:

if (document.getElementById) 

Isto vai permitir que outros browsers que suporte ao padrão W3C , assim como o Opera ou Safari, trabalherm sem mais alguma mudança.

Detecção por UserAgent, de qualquer modo, faz a diferença quando a exatidão é importante, assim como quando você estpa verificando que um browser reconhece os requerimentos da aplicação Web ou você está tentando trabalhar entorno de um bug.

JavaScript tambem segue as declarações condicionais, no qual pode auxiliar com a leitura do código.

var foo = (condição) ? condiçãoVerdadeira : condiçãoFalsa;

Por exemplo, para pegar um elemento, você usaria:

function getElement(aID){ 
   return (document.getElementById) ? document.getElementById(aID)
                                    : document.all[aID]);
 } 

Ou em outro caso poderia usar o operador || :

function getElement(aID){ 
   return (document.getElementById(aID)) || document.all[aID]);
 }

Diferenças entre Mozilla e Internet Explorer

Primeiramente, discutirei as diferenças que o caminho HTML comporta entre Mozilla e Internet Explorer.

Tipos de ferramentas

Os navegadores legados introduzem tipos de ferramentas HTML mostrando-as em links e usando o valor do atributo alt como um conteúdo tipo de ferramenta. A última especificação W3C HTML criou o atributo title, que é querido para conter um detalhada descrição do link. Navegadores modernos poderão usar o atributo title para exibir tipos de ferramentas, e Mozilla somente suporta mostrar tipos de ferramentas para este atributo e não o atributo alt.

Entidades

A marcação HTML pode conter severas entidades, que o corpo padrão web W3C tem definido. Você pode referenciar entidades através de sua referência numérica ou de caracteres. Por exemplo, você pode referenciar o caractere espaço em branco com o #160, com &#160; ou com o equivalente referencial de caractere &nbsp;.

Alguns navegadores mais antigos, como o Internet Explorer, teve tais peculiaridades que permitiam o uso de entidades substituindo o caractere ; (ponto e vírgula) no fim com um conteúdo regular no texto:

&nbsp Foo 
&nbsp&nbsp Foo 

Mozilla renderizará o acima &nbsp com espaços em branco, mesmo que isto esteja contra a especificação W3C. O navegador não analizará gramaticalmente um &nbsp se isto for diretamente seguido por mais caracteres, por exemplo:

&nbsp12345 

Este código não funciona no Mozilla, pois vai contra os padrões web do W3C. Sempre use a forma correta (&nbsp;) para evitar discrepâncias no navegador.

Diferenças do DOM

O Document Object Model (DOM) é a estrutura semelhante a uma árvore que contém os elementos do documento. Você pode manipular isto através de JavaScript, APIs, que o W3C tenha padronizado. Entretanto, prioritariamente à padronização W3C, o Netscape 4 e Internet Explorer 4 implementaram as APIs similarmente. Somente o Mozilla implementou legalmente APIs se elas forem de acordo com os padrões web W3C.

Acessando elementos

Para recuperar uma referência de elemento usando a aproxiamação do multi-navegador, você usa document.getElementById(aID), que trabalha em Internet Explorer 5.0+, navegadores baseados no Mozilla, outros navegadores complacentes ao W3C e é parte da especificação DOM Nível 1.

Mozilla não tem suporte total ao acesso de um elemento document.elementName ou mesmo pelo nome do elemento, o que o Internet Explorer faz (também chamado global namespace polluting). Mozilla também não suporta o método document.layers do Netscape 4 e o documenet.all do Internet Explorer. Enquanto document.getElementById deixa-o recuperar um elemento, você pode também usar document.layers e document.all para obter uma lista de todos os documentos com um determinado nome de etiqueta, tal como todos os elementos de <div>.

O método W3C DOM nível 1 pega referências para todos os elementos com o mesmo nome de etiqueta getElementsByTagName(). O método retorna um array em JavaScript, e pode ser chamado no elemento document ou em outros nós para buscar somente seus subníveis. Para conseguir um array de todos os elementos na árvore DOM, você pode usar getElementsByTagName("*").

Os métodos DOM nível 1, como mostrados na Tabela 1, são comumente usados para mover um elemento para uma certa posição e assegure sua visibilidade (menus, animações). O Netscape 4 usa a etiqueta <layer>, que o Mozilla não suporta, como um elemento HTML que pode ser posicionado em qualquer lugar. No Mozilla, você pode posicionar qualquer elemento usando a etiqueta <div>, que o Internet Explorer também usa e que você encontrará na especificação HTML.

Tabela 1. Métodos usados para acessar elementos
Método Descrição
document.getElementById( aId ) Retorna uma referência para o elemento com um ID espercificado.
document.getElementsByTagName( aTagName ) Retorna uma formação de elementos com o nome especificado no documento.

Manipule o DOM

O Mozilla suporta os W3C DOM APIs para manupular a árvore do DOM (veja a Tabela 2). Os APIs existem para cada nó no documento e permitem caminhar por esta árvore em qualquer direção. O Internet Explorer suporta bem estes APIs, mas ele também suporta seu métodos para andar pela árvore, como a propriedade children.

Table 2. Methods used to traverse the DOM
Propriedade/Método Descrição
childNodes Retorna um array de todos os nós filhos do elemento.
firstChild Retorna o primeiro nó do elemento.
getAttribute( umAtributo ) Retorna o valor do atributo especificado.
hasAttribute( umAtributo ) Retorna um valor boleano informando se o nó selecionado possúi o atributo especificado.
hasChildNodes() Retorna um valor boleano que informa se o nó atual possúi filhos.
lastChild Retorna o último nó do elemento.
nextSibling Retorna o o nó seguite a este.
nodeName Retorna o nome do atual nó como uma string.
nodeType Retorna o tipo do atual nó.
Value Description
1 Elemento
2 Atributo
3 Texto
4 Seção CDATA
5 Referencia de Entidade
6 Entidade
7 Processamento de Instrução
8 Comentário
9 Documento
10 Tipo de Documento
11 Fragmento de Documeto
12 Notação
nodeValue Retorna o valor do nó atual. Para nós que contém texto, tais como texto e comentários, será retornado seu valor como uma string. Para nós de atributo, o valor do atributo é retornado. Para todos os outros nós, o valor retornado é null.
ownerDocument Retorna o objeto document que comtém o nó atual.
parentNode Retorna o pai do nó selecionado.
previousSibling

Retorna o nó que está antes do nó selecionado (contrário de nextSibling).

removeAttribute( umNome ) Remove o atributo especificado do nó atual.
setAttribute( umNome, umValor ) Configura o valor do atributo especificado com o valor especificado.

O Internet Explorer tem um capricho fora do padrão, ele salta os nós de texto de espaços em branco que são gerados, por exemplo, para carácteres de nova linha. O Mozilla não salta, então algumas vezes voê terá de distinguir. Todos os nós têm a propriedade nodeType especificando seu tipo. Por exemplo, um nó de elemento tem o tipo 1, enquanto um nó de texto tem o tipo 3 e um comentário tem o tipo 8. A melhor maneira para processar apenas os nós de elementos é selecionar todos os nós filhos e só processar os nós com nodeType sendo 1:

HTML: 
  <div id="foo">
    <span>Teste</span>
  </div>

JavaScript: 
  var myDiv = document.getElementById("foo"); 
  var myChildren = myXMLDoc.childNodes; 
  for (var i = 0; i < myChildren.length; i++) { 
    if (myChildren[i].nodeType == 1){ 
      // element node
    };
  };

Gerando e Manipulando Conteúdo

O Mozilla suporta os métodos antigos para a adição de conteúdo no DOM dinamicamente, como document.write, document.open e document.close. O Mozilla também suporta o método innerHTML do Internet Explorer, que podemos chamar em quase todos os nós. Contudo, não suporta o outerHTML (que acrescenta a marcação ao redor do elemento, e não há um padrão equivalente) e innerText (que configura o valor do texto do nó, e que você pode conseguir no Mozilla usando textContent).

O Internet Explorer temmétodos de manipulação de conteúdo rígidos qua não são padrão e não são suportadas no Mozilla, incluindo recuperação de valor, inserção de elementos e inserção de texto adjacente ao nó, tal como getAdjacentElement e insertAdjacentHTML. A Tabela 3 mostra os padrões W3C e Mozilla para manipulação de conteúdo, que são métodos para qualquer nó do DOM.

Tabela 3. Métodos que o Mozilla usa para manipular conteúdo
Método Descrição
appendChild( umNó ) Cria um novo nó filho. Retorna uma referencia para o novo nó.
cloneNode( aDeep ) Faz uma cópia do nó quando é chamado e retorna a cópia. Se aDeep for true, é copiado o nó com sua subárvore.
createElement( umaTag ) Cria e retorna um nó do DOM sem pai do tipo especificado em umaTag.
createTextNode( umTexto ) Cria e retorna um nó de texto do DOM sem pai com o valor especificado em umTexto.
insertBefore( novoNó, umNó ) Insere novoNó antes de umNó.
removeChild( nóFilho ) Remove nóFilho e retorna uma referência para ele.
replaceChild( novoNó, nóFilho ) Troca nóFilho por novoNó e retorna uma referência para o nó removido.

Document fragments

For performance reasons, you can create documents in memory, rather than working on the existing document's DOM. DOM Level 1 Core introduced document fragments, which are lightweight documents that contain a subset of a normal document's interfaces. For example, getElementById does not exist, but appendChild does. You can also easily add document fragments to existing documents.

Mozilla creates document fragments through document.createDocumentFragment(), which returns an empty document fragment.

Internet Explorer's implementation of document fragments, however, does not comply with the W3C web standards and simply returns a regular document.

JavaScript differences

Most differences between Mozilla and Internet Explorer are usually blamed on JavaScript. However, the issues usually lie in the APIs that a browser exposes to JavaScript, such as the DOM hooks. The two browsers possess few core JavaScript differences; issues encountered are often timing related.

JavaScript date differences

The only Date difference is the getYear method. As per the ECMAScript specification (which is the specification JavaScript follows), the method is not Y2k-compliant, and running new Date().getYear() in 2004 will return "104". Per the ECMAScript specification, getYear returns the year minus 1900, originally meant to return "98" for 1998. getYear was deprecated in ECMAScript Version 3 and replaced with getFullYear(). Internet Explorer changed getYear() to work like getFullYear() and make it Y2k-compliant, while Mozilla kept the standard behavior.

JavaScript execution differences

Different browsers execute JavaScript differently. For example, the following code assumes that the div node already exists in the DOM by the time the script block executes:

...
<div id="foo">Loading...</div>

<script> 
  document.getElementById("foo").innerHTML = "Done."; 
</script> 

However, this is not guaranteed. To be sure that all elements exist, you should use the onload event handler on the <body> tag:

<body onload="doFinish();"> 

<div id="foo">Loading...</div> 

<script> 
  function doFinish() { 
    var element = document.getElementById("foo");
    element.innerHTML = "Done."; 
  }
</script> 
... 

Such timing-related issues are also hardware-related -- slower systems can reveal bugs that faster systems hide. One concrete example is window.open, which opens a new window:

<script> 
  function doOpenWindow(){ 
    var myWindow = window.open("about:blank"); 
    myWindow.location.href = "http://www.ibm.com"; 
  }
</script> 

The problem with the code is that window.open is asynchronous -- it does not block the JavaScript execution until the window has finished loading. Therefore, you may execute the line after the window.open line before the new window has finished. You can deal with this by having an onload handler in the new window and then call back into the opener window (using window.opener).

Differences in JavaScript-generating HTML

JavaScript can, through document.write, generate HTML on the fly from a string. The main issue here is when JavaScript, embedded inside an HTML document (thus, inside an <script> tag), generates HTML that contains a <script> tag. If the document is in strict rendering mode, it will parse the </script> inside the string as the closing tag for the enclosing <script>. The following code illustrates this best:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
... 
<script> 
  document.write("<script type='text\/javascript'>alert('Hello');<\/script>") 
</script> 

Since the page is in strict mode, Mozilla's parser will see the first <script> and parse until it finds a closing tag for it, which would be the first </script>. This is because the parser has no knowledge about JavaScript (or any other language) when in strict mode. In quirks mode, the parser is aware of JavaScript when parsing (which slows it down). Internet Explorer is always in quirks mode, as it does not support true XHTML. To make this work in strict mode in Mozilla, separate the string into two parts:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
... 
<script> 
  document.write("<script type='text\/javascript'>alert('Hello');</" + "script>") 
</script> 

Debug JavaScript

Mozilla provides several ways to debug JavaScript-related issues found in applications created for Internet Explorer. The first tool is the built-in JavaScript console, shown in Figure 1, where errors and warnings are logged. You can access it in Mozilla by going to Tools -> Web Development -> JavaScript Console or in Firefox (the standalone browser product from Mozilla) at Tools -> JavaScript Console.

Figure 1. JavaScript console

Javascript Console

The JavaScript console can show the full log list or just errors, warnings, and messages. The error message in Figure 1 says that at aol.com, line 95 tries to access an undefined variable called is_ns70. Clicking on the link will open Mozilla's internal view source window with the offending line highlighted.

The console also allows you to evaluate JavaScript. To evaluate the entered JavaScript syntax, type in 1+1 into the input field and press Evaluate, as Figure 2 shows.

Figure 2. JavaScript console evaluating

JavaScript Console evaluating

Mozilla's JavaScript engine has built-in support for debugging, and thus can provide powerful tools for JavaScript developers. Venkman, shown in Figure 3, is a powerful, cross-platform JavaScript debugger that integrates with Mozilla. It is usually bundled with Mozilla releases; you can find it at Tools -> Web Development -> JavaScript Debugger. For Firefox, the debugger isn't bundled; instead, you can download and install it from the Venkman Project Page. You can also find tutorials at the development page, located at the Venkman Development Page.

Figure 3. Mozilla's JavaScript debugger

Mozilla's JavaScript debugger

The JavaScript debugger can debug JavaScript running in the Mozilla browser window. It supports such standard debugging features as breakpoint management, call stack inspection, and variable/object inspection. All features are accessible through the user interface or through the debugger's interactive console. With the console, you can execute arbitrary JavaScript in the same scope as the JavaScript currently being debugged.

CSS differences

Mozilla-based products have the strongest support for Cascading Style Sheets (CSS), including most of CSS1, CSS2.1 and parts of CSS3, compared to Internet Explorer as well as all other browsers.

For most issues mentioned below, Mozilla will add an error or warning entry into the JavaScript console. Check the JavaScript console if you encounter CSS-related issues.

Mimetypes (when CSS files are not applied)

The most common CSS-related issue is that CSS definitions inside referenced CSS files are not applied. This is usually due to the server sending the wrong mimetype for the CSS file. The CSS specification states that CSS files should be served with the text/css mimetype. Mozilla will respect this and only load CSS files with that mimetype if the Web page is in strict standards mode. Internet Explorer will always load the CSS file, no matter with which mimetype it is served. Web pages are considered in strict standards mode when they start with a strict doctype. To solve this problem, you can make the server send the right mimetype or remove the doctype. I'll discuss more about doctypes in the next section.

CSS and units

Many Web applications do not use units with their CSS, especially when you use JavaScript to set the CSS. Mozilla tolerates this, as long as the page is not rendered in strict mode. Since Internet Explorer does not support true XHTML, it does not care if no units are specified. If the page is in strict standards mode, and no units are used, then Mozilla ignores the style:

<DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 
  "http://www.w3.org/TR/html4/strict.dtd"> 
<html> 
  <head> 
   <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
   <title>CSS and units example</title> 
  </head> 
  <body> 
    // works in strict mode 
    <div style="width: 40px; border: 1px solid black;">
      Text
    </div>

    // will fail in strict mode 
    <div style="width: 40; border: 1px solid black;">
      Text
    </div>
  </body> 
</html> 

Since the above example has a strict doctype, the page is rendered in strict standards mode. The first div will have a width of 40px, since it uses units, but the second div won't get a width, and thus will default to 100% width. The same would apply if the width were set through JavaScript.

JavaScript and CSS

Since Mozilla supports the CSS standards, it also supports the CSS DOM standard for setting CSS through JavaScript. You can access, remove, and change an element's CSS rules through the element's style member:

<div id="myDiv" style="border: 1px solid black;">
  Text
</div>

<script>
  var myElm = document.getElementById("myDiv"); 
  myElm.style.width = "40px"; 
</script>

You can reach every CSS attribute that way. Again, if the Web page is in strict mode, you must set a unit or else Mozilla will ignore the command. When you query a value, say through .style.width, in Mozilla and Internet Explorer, the returned value will contain the unit, meaning a string is returned. You can convert the string into a number through parseFloat("40px").

CSS overflow differences

CSS added the notion of overflow, which allows you to define how to handle overflow; for example, when the contents of a div with a specified height are taller than that height. The CSS standard defines that if no overflow behavior is set in this case, the div contents will overflow. However, Internet Explorer does not comply with this and will expand the div beyond its set height in order to hold the contents. Below is an example that shows this difference:

<div style="height: 100px; border: 1px solid black;">
  <div style="height: 150px; border: 1px solid red; margin: 10px;">
    a
  </div>
</div>

As you can see in Figure 4, Mozilla acts like the W3C standard specifies. The W3C standard says that, in this case, the inner div overflows to the bottom since the inner content is taller than its parent. If you prefer the Internet Explorer behavior, simply do not specify a height on the outer element.

Figure 4. DIV overflow

DIV Overflow

hover differences

The nonstandard CSS hover behavior in Internet Explorer occurs on quite a few web sites. It usually manifests itself by changing text style when hovered over in Mozilla, but not in Internet Explorer. This is because the a:hover CSS selector in Internet Explorer matches <a href="">...</a> but not <a name="">...</a>, which sets anchors in HTML. The text changes occur because authors encapsulate the areas with the anchor-setting markup:

CSS:
  a:hover {color: green;}

HTML:
  <a href="foo.com">This text should turn green when you hover over it.</a>

  <a name="anchor-name">
    This text should change color when hovered over, but doesn't
    in Internet Explorer.
  </a>

Mozilla follows the CSS specification correctly and will change the color to green in this example. You can use two ways to make Mozilla behave like Internet Explorer and not change the color of the text when hovered over:

  • First, you can change the CSS rule to be a:link:hover {color: green;}, which will only change the color if the element is a link (has an href attribute).
  • Alternatively, you can change the markup and close the opened <a /> before the start of the text -- the anchor will continue to work this way.

Quirks versus standards mode

Older legacy browsers, such as Internet Explorer 4, rendered with so-called quirks under certain conditions. While Mozilla aims to be a standards-compliant browser, it has three modes that support older Web pages created with these quirky behaviors. The page's content and delivery determine which mode Mozilla will use. Mozilla will indicate the rendering mode in View -> Page Info (or <kbd>Ctrl+I</kbd>) ; Firefox will list the rendering mode in Tools -> Page Info. The mode in which a page is located depends on its doctype.

Doctypes (short for document type declarations) look like this:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

The section in blue is called the public identifier, the green part is the system identifier, which is a URI.

Standards mode

Standards mode is the strictest rendering mode -- it will render pages per the W3C HTML and CSS specifications and will not support any quirks. Mozilla uses it for the following conditions:

  • If a page is sent with a text/xml mimetype or any other XML or XHTML mimetype
  • For any "DOCTYPE HTML SYSTEM" doctype (for example, <!DOCTYPE HTML SYSTEM "http://www.w3.org/TR/REC-html40/strict.dtd">), except for the IBM doctype
  • For unknown doctypes or doctypes without DTDs

Almost standards mode

Mozilla introduced almost standards mode for one reason: a section in the CSS 2 specification breaks designs based on a precise layout of small images in table cells. Instead of forming one image to the user, each small image ends up with a gap next to it. The old IBM homepage shown in Figure 5 offers an example.

Figure 5. Image gap

Image Gap

Almost standards mode behaves almost exactly as standards mode, except when it comes to an image gap issue. The issue occurs often on standards-compliant pages and causes them to display incorrectly.

Mozilla uses almost standards mode for the following conditions:

  • For any "loose" doctype (for example, <!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">, <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">)
  • For the IBM doctype (<!DOCTYPE html SYSTEM "http://www.ibm.com/data/dtd/v11/ibmxhtml1-transitional.dtd">)

You can read more about the image gap issue.

Quirks mode

Currently, the Web is full of invalid HTML markup, as well as markup that only functions due to bugs in browsers. The old Netscape browsers, when they were the market leaders, had bugs. When Internet Explorer arrived, it mimicked those bugs in order to work with the content at that time. As newer browsers came to market, most of these original bugs, usually called quirks, were kept for backwards compatibility. Mozilla supports many of these in its quirks rendering mode. Note that due to these quirks, pages will render slower than if they were fully standards-compliant. Most Web pages are rendered under this mode.

Mozilla uses quirks mode for the following conditions:

  • When no doctype is specified
  • For doctypes without a system identifier (for example, <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">)

For further reading, check out: Mozilla Quirks Mode Behavior and Mozilla's DOCTYPE sniffing.

Event differences

Mozilla and Internet Explorer are almost completely different in the area of events. The Mozilla event model follows the W3C and Netscape model. In Internet Explorer, if a function is called from an event, it can access the event object through window.event. Mozilla passes an event object to event handlers. They must specifically pass the object on to the function called through an argument.

A cross-browser event handling example follows (note that it means you can't define a global variable named event in your code):

<div onclick="handleEvent(event);">Click me!</div>

<script>
  function handleEvent(aEvent) { 
    var myEvent = window.event ? window.event : aEvent;
  }
</script>

The properties and functions that the event object exposes are also often named differently in Mozilla and Internet Explorer, as Table 4 shows.

Table 4. Event properties differences between Mozilla and Internet Explorer
Internet Explorer Name Mozilla Name Description
altKey altKey Boolean property that returns whether the alt key was pressed during the event.
cancelBubble stopPropagation() Used to stop the event from bubbling farther up the tree.
clientX clientX The X coordinate of the event, in relation to the element viewport.
clientY clientY The Y coordinate of the event, in relation to the element viewport.
ctrlKey ctrlKey Boolean property that returns whether the Ctrl key was pressed during the event.
fromElement relatedTarget For mouse events, this is the element from which the mouse moved away.
keyCode keyCode For keyboard events, this is a number representing the key that was pressed. It is 0 for mouse events. For keypress events (not keydown/keyup) of keys that produce output, the Mozilla equivalent is charCode, not keyCode.
returnValue preventDefault() Used to prevent the event's default action from occurring.
screenX screenX The X coordinate of the event, in relation to the screen.
screenY screenY The Y coordinate of the event, in relation to the screen.
shiftKey shiftKey Boolean property that returns whether the Shift key was pressed during the event.
srcElement target The element to which the event was originally dispatched.
toElement currentTarget For mouse events, this is the element to which the mouse moved.
type type Returns the name of the event.

Attach event handlers

Mozilla supports two ways to attach events through JavaScript. The first, supported by all browsers, sets event properties directly on objects. To set a click event handler, a function reference is passed to the object's onclick property:

<div id="myDiv">Click me!</div>

<script>
  function handleEvent(aEvent) {
    // if aEvent is null, means the Internet Explorer event model,
    // so get window.event.
    var myEvent = aEvent ? aEvent : window.event;
  }

  function onPageLoad(){
    document.getElementById("myDiv").onclick = handleEvent;
  } 
</script>

Mozilla fully supports the W3C standard way of attaching listeners to DOM nodes. You use the addEventListener() and removeEventListener() methods, and have the benefit of being able to set multiple listeners for the same event type. Both methods require three parameters: the event type, a function reference, and a boolean denoting whether the listener should catch events in their capture phase. If the boolean is set to false, it will only catch bubbling events. W3C events have three phases: capturing, at target, and bubbling. Every event object has an eventPhase attribute indicating the phase numerically (0 indexed). Every time you trigger an event, the event starts at the DOM's outermost element, the element at the top of the DOM tree. It then walks the DOM using the most direct route toward the target, which is the capturing phase. When the event reaches the target, the event is in the target phase. After arriving at the target, it walks up the DOM tree back to the outermost node; this is bubbling. Internet Explorer's event model only has the bubbling phase; therefore, setting the third parameter to false results in Internet Explorer-like behavior:

<div id="myDiv">Click me!</div> 

<script> 

  function handleEvent(aEvent) {
    // if aEvent is null, it is the Internet Explorer event model,
    // so get window.event.
    var myEvent = aEvent ? aEvent : window.event;
  }

  function onPageLoad() {
    var element = document.getElementById("myDiv");
    element.addEventListener("click", handleEvent, false);
  }
</script>

One advantage of addEventListener() and removeEventListener() over setting properties is that you can have multiple event listeners for the same event, each calling another function. Thus, to remove an event listener requires all three parameters be the same as the ones you use when adding the listener.

Mozilla does not support Internet Explorer's method of converting <script> tags into event handlers, which extends <script> with for and event attributes (see Table 5). It also does not support the attachEvent and detachEvent methods. Instead, you should use the addEventListener and removeEventListener methods. Internet Explorer does not support the W3C events specification.

Table 5. Event method differences between Mozilla and Internet Explorer
Internet Explorer Method Mozilla Method Description
attachEvent(aEventType, aFunctionReference) addEventListener(aEventType, aFunctionReference, aUseCapture) Adds an event listener to a DOM element.
detachEvent(aEventType, aFunctionReference) removeEventListener(aEventType, aFunctionReference, aUseCapture) Removes an event listener to a DOM element.

Rich text editing

While Mozilla prides itself with being the most W3C web standards compliant browser, it does support nonstandard functionality, such as innerHTML and rich text editing, if no W3C equivalent exists.

Mozilla 1.3 introduced an implementation of Internet Explorer's designMode feature, which turns an HTML document into a rich text editor field. Once turned into the editor, commands can run on the document through the execCommand command. Mozilla does not support Internet Explorer's contentEditable attribute for making any widget editable. You can use an iframe to add a rich text editor.

Rich text differences

Mozilla supports the W3C standard of accessing iframe's document object through IFrameElmRef.contentDocument, while Internet Explorer requires you to access it through document.frames{{ mediawiki.external('\"IframeName\"') }} and then access the resulting document:

<script>
function getIFrameDocument(aID) {
  var rv = null; 

  // if contentDocument exists, W3C compliant (Mozilla)
  if (document.getElementById(aID).contentDocument){
    rv = document.getElementById(aID).contentDocument;
  } else {
    // IE
    rv = document.frames[aID].document;
  }
  return rv;
}
</script> 

Another difference between Mozilla and Internet Explorer is the HTML that the rich text editor creates. Mozilla defaults to using CSS for the generated markup. However, Mozilla allows you to toggle between HTML and CSS mode using the useCSS execCommand and toggling it between true and false. Internet Explorer always uses HTML markup.

Mozilla (CSS): 
  <span style="color: blue;">Big Blue</span> 

Mozilla (HTML): 
  <font color="blue">Big Blue</font> 

Internet Explorer: 
  <FONT color="blue">Big Blue</FONT> 

Below is a list of commands that execCommand in Mozilla supports:

Table 6. Rich text editing commands
Command Name Description Argument
bold Toggles the selection's bold attribute. ---
createlink Generates an HTML link from the selected text. The URL to use for the link
delete Deletes the selection. ---
fontname Changes the font used in the selected text. The font name to use (Arial, for example)
fontsize Changes the font size used in the selected text. The font size to use
fontcolor Changes the font color used in the selected text. The color to use
indent Indents the block where the caret is. ---
inserthorizontalrule Inserts an <hr> element at the cursor's position. ---
insertimage Inserts an image at the cursor's position. URL of the image to use
insertorderedlist Inserts an ordered list (<ol>) element at the cursor's position. ---
insertunorderedlist Inserts an unordered list (<ul>) element at the cursor's position. ---
italic Toggles the selection's italicize attribute. ---
justifycenter Centers the content at the current line. ---
justifyleft Justifies the content at the current line to the left. ---
justifyright Justifies the content at the current line to the right. ---
outdent Outdents the block where the caret is. ---
redo Redoes the previous undo command. ---
removeformat Removes all formatting from the selection. ---
selectall Selects everything in the rich text editor. ---
strikethrough Toggles the strikethrough of the selected text. ---
subscript Converts the current selection into subscript. ---
superscript Converts the current selection into superscript. ---
underline Toggles the underline of the selected text. ---
undo Undoes the last executed command. ---
unlink Removes all link information from the selection. ---
useCSS Toggles the usage of CSS in the generated markup. Boolean value

For more information, visit Rich-Text Editing in Mozilla.

XML differences

Mozilla has strong support for XML and XML-related technologies, such as XSLT and Web services. It also supports some non-standard Internet Explorer extensions, such as XMLHttpRequest.

How to handle XML

As with standard HTML, Mozilla supports the W3C XML DOM specification, which allows you to manipulate almost any aspect of an XML document. Differences between Internet Explorer's XML DOM and Mozilla are usually caused by Internet Explorer's nonstandard behaviors. Probably the most common difference is how they handle white space text nodes. Often when XML generates, it contains white spaces between XML nodes. Internet Explorer, when using Node.childNodes, will not contain these white space nodes. In Mozilla, those nodes will be in the array.

XML: 
  <?xml version="1.0"?> 
  <myXMLdoc xmlns:myns="http://myfoo.com"> 
    <myns:foo>bar</myns:foo> 
  </myXMLdoc>

JavaScript:
  var myXMLDoc = getXMLDocument().documentElement; 
  alert(myXMLDoc.childNodes.length); 

The first line of JavaScript loads the XML document and accesses the root element (myXMLDoc) by retrieving the documentElement. The second line simply alerts the number of child nodes. Per the W3C specification, the white spaces and new lines merge into one text node if they follow each other. For Mozilla, the myXMLdoc node has three children: a text node containing a new line and two spaces; the myns:foo node; and another text node with a new line. Internet Explorer, however, does not abide by this and will return "1" for the above code, namely only the myns:foo node. Therefore, to walk the child nodes and disregard text nodes, you must distinguish such nodes.

As mentioned earlier, every node has a nodeType property representing the node type. For example, an element node has type 1, while a document node has type 9. To disregard text nodes, you must check for types 3 (text node) and 8 (comment node).

XML:
  <?xml version="1.0"?>   
  <myXMLdoc xmlns:myns="http://myfoo.com"> 
    <myns:foo>bar</myns:foo> 
  </myXMLdoc>

JavaScript: 
  var myXMLDoc = getXMLDocument().documentElement; 
  var myChildren = myXMLDoc.childNodes; 

  for (var run = 0; run < myChildren.length; run++){ 
    if ( (myChildren[run].nodeType != 3) &&
          myChildren[run].nodeType != 8) ){ 
      // not a text or comment node 
    };
  };

See Whitespace in the DOM for more detailed discussion and a possible solution.

XML data islands

Internet Explorer has a nonstandard feature called XML data islands, which allow you to embed XML inside an HTML document using the nonstandard HTML tag <xml>. Mozilla does not support XML data islands and handles them as unknown HTML tags. You can achieve the same functionality using XHTML; however, because Internet Explorer's support for XHTML is weak, this is usually not an option.

IE XML data island:

<xml id="xmldataisland"> 
  <foo>bar</foo> 
</xml>

One cross-browser solution is to use DOM parsers, which parse a string that contains a serialized XML document and generates the document for the parsed XML. Mozilla uses the DOMParser object, which takes the serialized string and creates an XML document out of it. In Internet Explorer, you can achieve the same functionality using ActiveX. The object created using new ActiveXObject("Microsoft.XMLDOM") has a loadXML method that can take in a string and generate a document from it. The following code shows you how:

var xmlString = "<xml id=\"xmldataisland\"><foo>bar</foo></xml>"; 
var myDocument; 

if (window.DOMParser) {
  // This browser appears to support DOMParser
  var parser = new DOMParser(); 
  myDocument = parser.parseFromString(xmlString, "text/xml"); 
} else if (window.ActiveXObject){ 
  // Internet Explorer, create a new XML document using ActiveX 
  // and use loadXML as a DOM parser. 
  myDocument = new ActiveXObject("Microsoft.XMLDOM"); 
  myDocument.async = false; 

  myDocument.loadXML(xmlString);
} else {
  // Not supported.
}

See Using XML Data Islands in Mozilla for an alternative approach.

XMLHttpRequest

Internet Explorer allows you to send and retrieve XML files using MSXML's XMLHTTP class, which is instantiated through ActiveX using new ActiveXObject("Msxml2.XMLHTTP") or new ActiveXObject("Microsoft.XMLHTTP"). Since there is no standard method of doing this, Mozilla provides the same functionality in the global JavaScript XMLHttpRequest object. Since version 7 IE also supports the "native" XMLHttpRequest object.

After instantiating the object using new XMLHttpRequest(), you can use the open method to specify what type of request (GET or POST) you use, which file you load, and if it is asynchronous or not. If the call is asynchronous, then give the onload member a function reference, which is called once the request has completed.

Synchronous request:

var myXMLHTTPRequest = new XMLHttpRequest(); 
myXMLHTTPRequest.open("GET", "data.xml", false); 

myXMLHTTPRequest.send(null); 

var myXMLDocument = myXMLHTTPRequest.responseXML; 

Asynchronous request:

var myXMLHTTPRequest; 

function xmlLoaded() { 
  var myXMLDocument = myXMLHTTPRequest.responseXML; 
}

function loadXML(){ 
  myXMLHTTPRequest = new XMLHttpRequest();
  myXMLHTTPRequest.open("GET", "data.xml", true);
  myXMLHTTPRequest.onload = xmlLoaded; 
  myXMLHTTPRequest.send(null); 
}

Table 7 features a list of available methods and properties for Mozilla's XMLHttpRequest.

Table 7. XMLHttpRequest methods and properties
Name Description
void abort() Stops the request if it is still running.
string getAllResponseHeaders() Returns all response headers as one string.
string getResponseHeader(string headerName) Returns the value of the specified header.
functionRef onerror If set, the references function will be called whenever an error occurs during the request.
functionRef onload If set, the references function will be called when the request completes successfully and the response has been received. Use when an asynchronous request is used.
void open (string HTTP_Method, string URL)

void open (string HTTP_Method, string URL, boolean async, string userName, string password)
Initializes the request for the specified URL, using either GET or POST as the HTTP method. To send the request, call the send() method after initialization. If async is false, the request is synchronous, else it defaults to asynchronous. Optionally, you can specify a username and password for the given URL needed.
int readyState State of the request. Possible values:
Value Description
0 UNINITIALIZED - open() has not been called yet.
1 LOADING - send() has not been called yet.
2 LOADED - send() has been called, headers and status are available.
3 INTERACTIVE - Downloading, responseText holds the partial data.
4 COMPLETED - Finished with all operations.
string responseText String containing the response.
DOMDocument responseXML DOM Document containing the response.
void send(variant body) Initiates the request. If body is defined, it is sent as the body of the POST request. body can be an XML document or a string serialized XML document.
void setRequestHeader (string headerName, string headerValue) Sets an HTTP request header for use in the HTTP request. Has to be called after open() is called.
string status The status code of the HTTP response.

XSLT differences

Mozilla supports XSL Transformations (XSLT) 1.0. It also allows JavaScript to perform XSLT transformations and allows running XPath on a document.

Mozilla requires that you send the XML and XSLT files with an XML mimetype (text/xml or application/xml). This is the most common reason why XSLT won't run in Mozilla but will in Internet Explorer. Mozilla is strict in that way.

Internet Explorer 5.0 and 5.5 supported XSLT's working draft, which is substantially different than the final 1.0 recommendation. The easiest way to distinguish what version an XSLT file was written against is to look at the namespace. The namespace for the 1.0 recommendation is http://www.w3.org/1999/XSL/Transform, while the working draft's namespace is http://www.w3.org/TR/WD-xsl. Internet Explorer 6 supports the working draft for backwards compatibility, but Mozilla does not support the working draft, only the final recommendation.

If XSLT requires you to distinguish the browser, you can query the "xsl:vendor" system property. Mozilla's XSLT engine will report itself as "Transformiix" and Internet Explorer will return "Microsoft".

<xsl:if test="system-property('xsl:vendor') = 'Transformiix'"> 
  <!-- Mozilla specific markup --> 
</xsl:if> 
<xsl:if test="system-property('xsl:vendor') = 'Microsoft'"> 
  <!-- Internet Explorer specific markup --> 
</xsl:if> 

Mozilla also provides JavaScript interfaces for XSLT, allowing a Web site to complete XSLT transformations in memory. You can do this using the global XSLTProcessor JavaScript object. XSLTProcessor requires you to load the XML and XSLT files, because it needs their DOM documents. The XSLT document, imported by the XSLTProcessor, allows you to manipulate XSLT parameters.

XSLTProcessor can generate a standalone document using transformToDocument(), or it can create a document fragment using transformToFragment(), which you can easily append into another DOM document. Below is an example:

var xslStylesheet; 
var xsltProcessor = new XSLTProcessor(); 

// load the xslt file, example1.xsl 
var myXMLHTTPRequest = new XMLHttpRequest(); 
myXMLHTTPRequest.open("GET", "example1.xsl", false); 
myXMLHTTPRequest.send(null); 

// get the XML document and import it 
xslStylesheet = myXMLHTTPRequest.responseXML; 

xsltProcessor.importStylesheet(xslStylesheet); 

// load the xml file, example1.xml 
myXMLHTTPRequest = new XMLHttpRequest(); 
myXMLHTTPRequest.open("GET", "example1.xml", false); 
myXMLHTTPRequest.send(null); 

var xmlSource = myXMLHTTPRequest.responseXML; 

var resultDocument = xsltProcessor.transformToDocument(xmlSource); 

After creating an XSLTProcessor, you load the XSLT file using XMLHttpRequest. The XMLHttpRequest's responseXML member contains the XML document of the XSLT file, which is passed to importStylesheet. You then use the XMLHttpRequest again to load the source XML document that must be transformed; that document is then passed to the transformToDocument method of XSLTProcessor. Table 8 features a list of XSLTProcessor methods.

Table 8. XSLTProcessor methods
Method Description
void importStylesheet(Node styleSheet) Imports the XSLT stylesheet. The styleSheet argument is the root node of an XSLT stylesheet's DOM document.
DocumentFragment transformToFragment(Node source, Document owner) Transforms the Node source by applying the stylesheet imported using the importStylesheet method and generates a DocumentFragment. owner specifies what DOM document the DocumentFragment should belong to, making it appendable to that DOM document.
Document transformToDocument(Node source) Transforms the Node source by applying the stylesheet imported using the importStylesheet method and returns a standalone DOM document.
void setParameter(String namespaceURI, String localName, Variant value) Sets a parameter in the imported XSLT stylesheet.
Variant getParameter(String namespaceURI, String localName) Gets the value of a parameter in the imported XSLT stylesheet.
void removeParameter(String namespaceURI, String localName) Removes all set parameters from the imported XSLT stylesheet and makes them default to the XSLT-defined defaults.
void clearParameters() Removes all set parameters and sets them to defaults specified in the XSLT stylesheet.
void reset() Removes all parameters and stylesheets.

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