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HTMLTextAreaElement - Web API | MDN

Baseline Widely available *

HTMLTextAreaElement 接口提供了特殊的属性和方法，用于控制 <textarea> 元素的布局和展示。

must be a string

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.

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.

Listen to these events using addEventListener() or by assigning an event listener to the oneventname property of this interface:

input 事件

Fires when the value of an <input>, <select>, or <textarea> element has been changed.

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 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>

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>

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