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HTMLTextAreaElement

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Inheritance Hierarchy: 
Node  <==  Element  <==  HTMLElement  <==  HTMLTextAreaElement,

HTMLTextAreaElement 接口提供了特殊的属性和方法用于操作“textarea”元素的布局和介绍。

属性

form 只读 object: 返回一个父表单元素的引用。如果这个元素没有被包含在一个表单元素中,则这个值是页面中任意一<form>元素的id 属性或者是一个null值。
type 只读 string: 返回字符串textarea。
value string: Returns / Sets the raw value contained in the control.
textLength 只读 long: Returns the codepoint length of the control's value. Same as calling value.length
defaultValue string: Returns / Sets the control's default value, which behaves like the Node.textContent property.
placeholder string: 返回/设置元素placeholder 属性, 用于提示用户在组件中应该输入什么。
rows unsigned long: Returns / Sets the element's rows attribute, indicating the number of visible text lines for the control.
cols unsigned long: Returns / Sets the element's cols attribute, indicating the visible width of the text area.
autofocus boolean: Returns / Sets the element's autofocus attribute, indicating that the control should have input focus when the page loads
name string: Returns / Sets the element's name attribute, containing the name of the control.
disabled boolean: Returns / Sets the element's disabled attribute, indicating that the control is not available for interaction.
maxLength long: Returns / Sets the element's maxlength attribute, indicating the maximum number of characters the user can enter. This constraint is evaluated only when the value changes.
accessKey string: Returns / Sets the element's accesskey attribute.
readOnly boolean: Returns / Sets the element's readonly attribute, indicating that the user cannot modify the value of the control.
required boolean: Returns / Sets the element's required attribute, indicating that the user must specify a value before submitting the form.
tabIndex long: Returns / Sets the position of the element in the tabbing navigation order for the current document.
selectionStart unsigned long: Returns / Sets the index of the beginning of selected text. If no text is selected, contains the index of the character that follows the input cursor. On being set, the control behaves as if setSelectionRange() had been called with this as the first argument, and selectionEnd as the second argument.
selectionEnd unsigned long: Returns / Sets the index of the end of selected text. If no text is selected, contains the index of the character that follows the input cursor. On being set, the control behaves as if setSelectionRange() had been called with this as the second argument, and selectionStart as the first argument.
selectionDirection string: Returns / Sets the direction in which selection occurred. This is "forward" if selection was performed in the start-to-end direction of the current locale, or "backward" for the opposite direction. This can also be "none" if the direction is unknown."
validity 只读 ValidityState object: Returns the validity states that this element is in.
willValidate 只读

boolean: Returns / Sets whether the element is a candidate for constraint validation. false if any conditions bar it from constraint validation.

validationMessage 只读 string: Returns a localized message that describes the validation constraints that the control does not satisfy (if any). This is the empty string if the control is not a candidate for constraint validation (willValidate is false), or it satisfies its constraints.
autocomplete  
autocapitalize string: Returns / Sets the element's capitalization behavior for user input. Valid values are: none, off, characters, words, sentences.
inputMode  
wrap string: Returns / Sets the wrap HTML attribute, indicating how the control wraps text.

The two properties tabIndex and accessKey are inherited from HTMLElement from HTML5 on, but were defined on HTMLTextAreaElement in DOM Level 2 HTML and earlier specifications.

Methods

focus() Gives focus to this control.
blur() Removes focus from this control.
select() Selects the contents of the control.
checkValidity() Returns false if the button is a candidate for constraint validation, and it does not satisfy its constraints. In this case, it also fires an invalid event at the control. It returns true if the control is not a candidate for constraint validation, or if it satisfies its constraints.
setCustomValidity(string) Sets a custom validity message for the element. If this message is not the empty string, then the element is suffering from a custom validity error, and does not validate.
setSelectionRange(selectionStart, selectionEnd, [optional] selectionDirection) Selects a range of text, and sets selectionStart and selectionEnd. If either argument is greater than the length of the value, it is treated as pointing to the end of the value. If end is less than start, then both are treated as the value of end.
setRangeText()  

The two methods blur() and focus() are inherited from HTMLElement from HTML5 on, but were defined on HTMLTextAreaElement in DOM Level 2 HTML and earlier specifications.

Examples

Autogrowing textarea example

Make a textarea autogrow while typing:

JavaScript function:

function autoGrow (oField) {
  if (oField.scrollHeight > oField.clientHeight) {
    oField.style.height = oField.scrollHeight + "px";
  }
}

CSS:

textarea.noscrollbars {
  overflow: hidden;
  width: 300px;
  height: 100px;
}

HTML:

<form>
  <fieldset>  
    <legend>Your comments</legend>  
    <p><textarea class="noscrollbars" onkeyup="autoGrow(this);"></textarea></p>
    <p><input type="submit" value="Send" /></p>
  </fieldset>
</form>

Insert HTML tags example

Insert some HTML tags or smiles or any custom text in a textarea.
JavaScript function:

function insertMetachars(sStartTag, sEndTag) {
  var bDouble = arguments.length > 1, oMsgInput = document.myForm.myTxtArea, nSelStart = oMsgInput.selectionStart, nSelEnd = oMsgInput.selectionEnd, sOldText = oMsgInput.value;
  oMsgInput.value = sOldText.substring(0, nSelStart) + (bDouble ? sStartTag + sOldText.substring(nSelStart, nSelEnd) + sEndTag : sStartTag) + sOldText.substring(nSelEnd);
  oMsgInput.setSelectionRange(bDouble || nSelStart === nSelEnd ? nSelStart + sStartTag.length : nSelStart, (bDouble ? nSelEnd : nSelStart) + sStartTag.length);
  oMsgInput.focus();
}

CSS to decorate the internal span to behave like a link:

.intLink {
  cursor: pointer;
  text-decoration: underline;
  color: #0000ff;
}

HTML:

<form name="myForm">
<p>[&nbsp;<span class="intLink" onclick="insertMetachars('&lt;strong&gt;','&lt;\/strong&gt;');"><strong>Bold</strong></span> | <span class="intLink" onclick="insertMetachars('&lt;em&gt;','&lt;\/em&gt;');"><em>Italic</em></span> | <span class="intLink" onclick="var newURL=prompt('Enter the full URL for the link');if(newURL){insertMetachars('&lt;a href=\u0022'+newURL+'\u0022&gt;','&lt;\/a&gt;');}else{document.myForm.myTxtArea.focus();}">URL</span> | <span class="intLink" onclick="insertMetachars('\n&lt;code&gt;\n','\n&lt;\/code&gt;\n');">code</span> | <span class="intLink" onclick="insertMetachars(' :-)');">smile</span> | etc. etc.&nbsp;]</p>
<p><textarea name="myTxtArea" rows="10" cols="50">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut facilisis, arcu vitae adipiscing placerat, nisl lectus accumsan nisi, vitae iaculis sem neque vel lectus. Praesent tristique commodo lorem quis fringilla. Sed ac tellus eros. Sed consectetur eleifend felis vitae luctus. Praesent sagittis, est eget bibendum tincidunt, ligula diam tincidunt augue, a fermentum odio velit eget mi. Phasellus mattis, elit id fringilla semper, orci magna cursus ligula, non venenatis lacus augue sit amet dui. Pellentesque lacinia odio id nisi pulvinar commodo tempus at odio. Ut consectetur eros porttitor nunc mollis ultrices. Aenean porttitor, purus sollicitudin viverra auctor, neque erat blandit sapien, sit amet tincidunt massa mi ac nibh. Proin nibh sem, bibendum ut placerat nec, cursus et lacus. Phasellus vel augue turpis. Nunc eu mauris eu leo blandit mollis interdum eget lorem. </textarea></p>
</form>

Maximum length and number of lines example

Create a textarea with a maximum number of characters per line and a maximum number of lines:

First, create a function that takes the text field and a key event as input and determines if any of the limits have been reached. If the limit has not been reached, it will return the key.

function checkRows(oField, oKeyEvent) {
  var nKey = (oKeyEvent || /* old IE */ window.event || /* check is not supported! */ { keyCode: 38 }).keyCode,

    // put here the maximum number of characters per line:
    nCols = 30,
    // put here the maximum number of lines:
    nRows = 5,

    nSelS = oField.selectionStart, nSelE = oField.selectionEnd,
    sVal = oField.value, nLen = sVal.length,

    nBackward = nSelS >= nCols ? nSelS - nCols : 0,
    nDeltaForw = sVal.substring(nBackward, nSelS).search(new RegExp("\\n(?!.{0," + String(nCols - 2) + "}\\n)")) + 1,
    nRowStart = nBackward + nDeltaForw,
    aReturns = (sVal.substring(0, nSelS) + sVal.substring(nSelE, sVal.length)).match(/\n/g),
    nRowEnd = nSelE + nRowStart + nCols - nSelS,
    sRow = sVal.substring(nRowStart, nSelS) + sVal.substring(nSelE, nRowEnd > nLen ? nLen : nRowEnd),
    bKeepCols = nKey === 13 || nLen + 1 < nCols || /\n/.test(sRow) || ((nRowStart === 0 || nDeltaForw > 0 || nKey > 0) && (sRow.length < nCols || (nKey > 0 && (nLen === nRowEnd || sVal.charAt(nRowEnd) === "\n"))));

  return (nKey !== 13 || (aReturns ? aReturns.length + 1 : 1) < nRows) && ((nKey > 32 && nKey < 41) || bKeepCols);
}

In the HTML we just need to hook our function to the `onkeypress` event and specify that our textarea does not accept pasting:

<form>
  <p>Textarea with fixed number of characters per line:<br />
    <textarea cols="50" rows="10" onkeypress="return checkRows(this, event);"
              onpaste="return false;"></textarea>
  </p>
</form>

Specifications

Specification Status Comment
WHATWG HTML Living Standard
HTMLTextAreaElement
Living Standard The following attributes have been added: autocomplete, and inputmode.
The following method has been added: setSelection().
HTML5
HTMLTextAreaElement
Recommendation The attributes tabindex and accesskey, as well as the methods blur() and focus() are now defined on HTMLElement.
The following attributes have been added: autofocus, placeholder, dirName, wrap, maxLength, required, textLength, labels, selectionStart, selectionEnd, selectionDirection, validity, validationMessage, and willValidate.
The following methods have been added: checkValidity(), setCustomValidity(), and setSelectionRange().
Document Object Model (DOM) Level 2 HTML Specification
HTMLTextAreaElement
Recommendation The property defaultValue doesn't contain the initial value of the value attribute, but the initial value of the content of the <textarea>.
Document Object Model (DOM) Level 1 Specification
HTMLTextAreaElement
Recommendation Initial definition

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support (Yes) (Yes) ? ? ? ?
autocapitalize 43.0 未实现 ? ? ? ?
textLength 47.0 未实现 28.0 (28.0) 未实现 33.0 9.0
Feature Android Chrome for Android Edge Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support ? (Yes) (Yes) (Yes) ? ? ?
autocapitalize 未实现 43.0 未实现 ? ? ? ?
textLength ? ? 未实现 ? ? ? ?

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