String

Sumário

O objeto global String  é um construtor para strings, ou uma sequência de caracteres.

Sintaxe

As formas literais de declaração de String  são:

'string text'
"string text"
"中文 español English हिन्दी العربية português বাংলা русский 日本語 ਪੰਜਾਬੀ 한국어"

Além da forma regular, de caracteres de impressão, caracteres especiais podem ser codificados usando a escape notation (notação com barra invertida):

Ou, usando o objeto global String diretamente:

String(thing)
new String(thing)

Parâmetros

thing

Anything to be converted to a string.

Descrição

Strings são úteis para guardar dados que podem ser representados em forma de texto. Uma das operações mais usadas nas strings é checar seu tamanho, para construir e concatená-las  usando os operadores + e +=, checando pela existência ou posição de substrings com o método indexOf , ou extrair substrings com o método substring.

Acesso à caractere

Há duas maneiras de acessar um caractere individual em uma string. A primeira é o método charAt:

return 'cat'.charAt(1); // returns "a"

A outra maneira (introduzido no ECMAScript 5) consiste em tratar a string como um objeto Array-like, onde os caráteres individuais correspondem a um índice numérico:

return 'cat'[1]; // returns "a"

For character access using bracket notation, attempting to delete or assign a value to these properties will not succeed. The properties involved are neither writable nor configurable. (See Object.defineProperty for more information.)

Comparando strings

Desenvolvedores de C têm a função strcmp() para comparar strings. No JavaScript, basta usar o operador maior que e menor que:

var a = "a";
var b = "b";
if (a < b) // true
  print(a + " is less than " + b);
else if (a > b)
  print(a + " is greater than " + b);
else
  print(a + " and " + b + " are equal.");

A similar result can be achieved using the localeCompare method inherited by String instances.

Distinçao entre String primitivas e String objetos

Note que o JavaScript distingue entre objetos String e valores de string primitivas. (O mesmo é válido para Boolean e Numbers.)

Strings literais (definidas por aspas duplas ou aspas simples) e strings retornadas da chamada da função String fora do contexto de uma função construtora (sem o uso da palavra chave new) são strings primitivas. O JavaScript converte automaticamente strings primitivas para objetos do tipo String, por isso é possível utilizar os métodos do objeto String através de strings primitivas. Em contextos onde um método é invocado de uma string primitiva ou uma propriedade é procurada, o JavaScript irá criar um objeto com a string primitiva e executar o método ou acessar a propriedade procurada.

var s_prim = "foo";
var s_obj = new String(s_prim);

console.log(typeof s_prim); // Logs "string"
console.log(typeof s_obj);  // Logs "object"

String primitives and String objects also give different results when using eval. Primitives passed to eval are treated as source code; String objects are treated as all other objects are, by returning the object. For example:

s1 = "2 + 2";               // creates a string primitive
s2 = new String("2 + 2");   // creates a String object
console.log(eval(s1));      // returns the number 4
console.log(eval(s2));      // returns the string "2 + 2"

For these reasons, code may break when it encounters String objects when it expects a primitive string instead, although generally authors need not worry about the distinction.

A String object can always be converted to its primitive counterpart with the valueOf method.

console.log(eval(s2.valueOf())); // returns the number 4

Propriedades

For properties available on String instances, see Properties of String instances.

String.prototype

Allows the addition of properties to a String object.

Metodos

For methods available on String instances, see Methods of String instances.

String.fromCharCode()

Returns a string created by using the specified sequence of Unicode values.

String.fromCodePoint()

Returns a string created by using the specified sequence of code points.

Metodos genericos de Strings

The String instance methods are also available in Firefox as of JavaScript 1.6 (though not part of the ECMAScript standard) on the String object for applying String methods to any object:

var num = 15;
alert(String.replace(num, /5/, '2'));

Generics are also available on Array methods.

The following is a shim to provide support to non-supporting browsers:

/*globals define*/
// Assumes all supplied String instance methods already present
// (one may use shims for these if not available)
(function () {
    'use strict';

    var i,
        // We could also build the array of methods with the following, but the
        //   getOwnPropertyNames() method is non-shimable:
        // Object.getOwnPropertyNames(String).filter(function (methodName)
        //  {return typeof String[methodName] === 'function'});
        methods = [
            'quote', 'substring', 'toLowerCase', 'toUpperCase', 'charAt',
            'charCodeAt', 'indexOf', 'lastIndexOf', 'startsWith', 'endsWith',
            'trim', 'trimLeft', 'trimRight', 'toLocaleLowerCase',
            'toLocaleUpperCase', 'localeCompare', 'match', 'search',
            'replace', 'split', 'substr', 'concat', 'slice'
        ],
        methodCount = methods.length,
        assignStringGeneric = function (methodName) {
            var method = String.prototype[methodName];
            String[methodName] = function (arg1) {
                return method.apply(arg1, Array.prototype.slice.call(arguments, 1));
            };
        };

    for (i = 0; i < methodCount; i++) {
        assignStringGeneric(methods[i]);
    }
}());

Instancia de String

Propriedades

String.prototype.constructor

Specifies the function that creates an object's prototype.

String.prototype.length

Reflects the length of the string.

N

Used to access the character in the Nth position where N is a positive integer between 0 and one less than the value of length. These properties are read-only.

Methods unrelated to HTML

String.prototype.charAt()

Returns the character at the specified index.

String.prototype.charCodeAt()

Returns a number indicating the Unicode value of the character at the given index.

String.prototype.codePointAt()

Returns a non-negative integer that is the UTF-16 encoded code point value at the given position.

String.prototype.concat()

Combines the text of two strings and returns a new string.

String.prototype.includes()

Determines whether one string may be found within another string.

String.prototype.endsWith()

Determines whether a string ends with the characters of another string.

String.prototype.indexOf()

Returns the index within the calling String object of the first occurrence of the specified value, or -1 if not found.

String.prototype.lastIndexOf()

Returns the index within the calling String object of the last occurrence of the specified value, or -1 if not found.

String.prototype.localeCompare()

Returns a number indicating whether a reference string comes before or after or is the same as the given string in sort order.

String.prototype.match()

Used to match a regular expression against a string.

String.prototype.normalize()

Returns the Unicode Normalization Form of the calling string value.

String.prototype.padEnd()

Pads the current string from the end with a given string to create a new string from a given length.

String.prototype.padStart()

Pads the current string from the start with a given string to create a new string from a given length.

String.prototype.quote()

Wraps the string in double quotes (""").

String.prototype.repeat()

Returns a string consisting of the elements of the object repeated the given times.

String.prototype.replace()

Used to find a match between a regular expression and a string, and to replace the matched substring with a new substring.

String.prototype.search()

Executes the search for a match between a regular expression and a specified string.

String.prototype.slice()

Extracts a section of a string and returns a new string.

String.prototype.split()

Splits a String object into an array of strings by separating the string into substrings.

String.prototype.startsWith()

Determines whether a string begins with the characters of another string.

String.prototype.substr()

Returns the characters in a string beginning at the specified location through the specified number of characters.

String.prototype.substring()

Returns the characters in a string between two indexes into the string.

String.prototype.toLocaleLowerCase()

The characters within a string are converted to lower case while respecting the current locale. For most languages, this will return the same as toLowerCase().

String.prototype.toLocaleUpperCase()

The characters within a string are converted to upper case while respecting the current locale. For most languages, this will return the same as toUpperCase().

String.prototype.toLowerCase()

Returns the calling string value converted to lower case.

String.prototype.toSource()

Returns an object literal representing the specified object; you can use this value to create a new object. Overrides the Object.prototype.toSource() method.

String.prototype.toString()

Returns a string representing the specified object. Overrides the Object.prototype.toString() method.

String.prototype.toUpperCase()

Returns the calling string value converted to uppercase.

String.prototype.trim()

Trims whitespace from the beginning and end of the string. Part of the ECMAScript 5 standard.

String.prototype.trimLeft()

Trims whitespace from the left side of the string.

String.prototype.trimRight()

Trims whitespace from the right side of the string.

String.prototype.valueOf()

Returns the primitive value of the specified object. Overrides the Object.prototype.valueOf() method.

String.prototype[@@iterator]()

Returns a new Iterator object that iterates over the code points of a String value, returning each code point as a String value.

HTML wrapper methods

These methods are of limited use, as they provide only a subset of the available HTML tags and attributes.

String.prototype.anchor()

<a name="name"> (hypertext target)

String.prototype.big()

<big>

String.prototype.blink()

<blink>

String.prototype.bold()

<b>

String.prototype.fixed()

<tt>

String.prototype.fontcolor()

<font color="color">

String.prototype.fontsize()

<font size="size">

String.prototype.italics()

<i>

String.prototype.link()

<a href="url"> (link to URL)

String.prototype.small()

<small>

String.prototype.strike()

<strike>

String.prototype.sub()

<sub>

String.prototype.sup()

<sup>

Exemplos

String conversion

It's possible to use String as a "safer" toString alternative, as although it still normally calls the underlying toString, it also works for null and undefined. For example:

var outputStrings = [];
for (let i = 0, n = inputValues.length; i < n; ++i) {
  outputStrings.push(String(inputValues[i]));
}

Especificaçoes

Compatibilidade de Browser

See also

• DOMString
• StringView – a C-like representation of strings based on typed arrays
• Binary strings