Element.getClientRects() - Web APIs 编辑

The getClientRects() method of the Element interface returns a collection of DOMRect objects that indicate the bounding rectangles for each CSS border box in a client.

Most elements only have one border box each, but a multiline inline element (such as a multiline <span> element, by default) has a border box around each line.

Syntax

let rectCollection = object.getClientRects();

Return value

The returned value is a collection of DOMRect objects, one for each CSS border box associated with the element. Each DOMRect object contains read-only left, top, right and bottom properties describing the border box, in pixels, with the top-left relative to the top-left of the viewport. For tables with captions, the caption is included even though it's outside the border box of the table. When called on SVG elements other than an outer-<svg>, the "viewport" that the resulting rectangles are relative to is the viewport that the element's outer-<svg> establishes (and to be clear, the rectangles are also transformed by the outer-<svg>'s viewBox transform, if any).

Originally, Microsoft intended this method to return a TextRectangle object for each line of text. However, the CSSOM working draft specifies that it returns a DOMRect for each border box. For an inline element, the two definitions are the same. But for a block element, Mozilla will return only a single rectangle.

Firefox 3.5 note

Firefox 3.5 adds width and height properties to the TextRectangle object.

The amount of scrolling that has been done of the viewport area (or any other scrollable element) is taken into account when computing the rectangles.

The returned rectangles do not include the bounds of any child elements that might happen to overflow.

For HTML <area> elements, SVG elements that do not render anything themselves, display:none elements, and generally any elements that are not directly rendered, an empty list is returned.

Rectangles are returned even for CSS boxes that have empty border-boxes. The left, top, right, and bottom coordinates can still be meaningful.

Fractional pixel offsets are possible.

Examples

These examples draw client rects in various colors. Note that the JavaScript function that paints the client rects is connected to the markup via the class withClientRectsOverlay.

HTML

Example 1: This HTML creates three paragraphs with a <span> inside, each embedded in a <div> block. Client rects are painted for the paragraph in the second block, and for the <span> element in the third block.

<h3>A paragraph with a span inside</h3>
<p>Both the span and the paragraph have a border set. The
  client rects are in red. Note that the p has onlyone border
  box, while the span has multiple border boxes.</p>

<div>
  <strong>Original</strong>
  <p>
    <span>Paragraph that spans multiple lines</span>
  </p>
</div>

<div>
  <strong>p's rect</strong>
  <p class="withClientRectsOverlay">
    <span>Paragraph that spans multiple lines</span>
  </p>
</div>

<div>
  <strong>span's rect</strong>
  <p>
    <span class="withClientRectsOverlay">Paragraph that spans multiple lines</span>
  </p>
</div>

Example 2: This HTML creates three ordered lists. Client rects are painted for the <ol> in the second block, and for each <li> element in the third block.

<h3>A list</h3>
<p>Note that the border box doesn't include the number, so
  neither do the client rects.</p>

<div>
  <strong>Original</strong>
  <ol>
    <li>Item 1</li>
    <li>Item 2</li>
  </ol>
</div>

<div>
  <strong>ol's rect</strong>
  <ol class="withClientRectsOverlay">
    <li>Item 1</li>
    <li>Item 2</li>
  </ol>
</div>

<div>
  <strong>each li's rect</strong>
  <ol>
    <li class="withClientRectsOverlay">Item 1</li>
    <li class="withClientRectsOverlay">Item 2</li>
  </ol>
</div>

Example 3: This HTML creates two tables with captions. Client rects are painted for the <table> in the second block.

<h3>A table with a caption</h3>
<p>Although the table's border box doesn't include the
  caption, the client rects do include the caption.</p>

<div>
  <strong>Original</strong>
  <table>
    <caption>caption</caption>
    <thead>
      <tr><th>thead</th></tr>
    </thead>
    <tbody>
      <tr><td>tbody</td></tr>
    </tbody>
  </table>
</div>

<div>
  <strong>table's rect</strong>
  <table class="withClientRectsOverlay">
    <caption>caption</caption>
    <thead>
      <tr><th>thead</th></tr>
    </thead>
    <tbody>
      <tr><td>tbody</td></tr>
    </tbody>
  </table>
</div>

CSS

The CSS draws borders around the paragraph and the <span> inside each <div> block for the first example, around the <ol> and <li> for the second example, and around <table>, <th>, and <td> elements for the third example.

strong {
  text-align: center;
}
div {
  display: inline-block;
  width: 150px;
}
div p, ol, table {
  border: 1px solid blue;
}
span, li, th, td {
  border: 1px solid green;
}

JavaScript

The JavaScript code draws the client rects for all HTML elements that have CSS class withClientRectsOverlay assigned.

function addClientRectsOverlay(elt) {
  /* Absolutely position a div over each client rect so that its border width
     is the same as the rectangle's width.
     Note: the overlays will be out of place if the user resizes or zooms. */
  var rects = elt.getClientRects();
  for (var i = 0; i != rects.length; i++) {
    var rect = rects[i];
    var tableRectDiv = document.createElement('div');
    tableRectDiv.style.position = 'absolute';
    tableRectDiv.style.border = '1px solid red';
    var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
    var scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft;
    tableRectDiv.style.margin = tableRectDiv.style.padding = '0';
    tableRectDiv.style.top = (rect.top + scrollTop) + 'px';
    tableRectDiv.style.left = (rect.left + scrollLeft) + 'px';
    // We want rect.width to be the border width, so content width is 2px less.
    tableRectDiv.style.width = (rect.width - 2) + 'px';
    tableRectDiv.style.height = (rect.height - 2) + 'px';
    document.body.appendChild(tableRectDiv);
  }
}

(function() {
  /* Call function addClientRectsOverlay(elt) for all elements with
     assigned class "withClientRectsOverlay" */
  var elt = document.getElementsByClassName('withClientRectsOverlay');
  for (var i = 0; i < elt.length; i++) {
    addClientRectsOverlay(elt[i]);
  }
})();

Result

Specifications

Notes

getClientRects() was first introduced in the MS IE DHTML object model.

Browser compatibility

BCD tables only load in the browser

See also

• Element.getBoundingClientRect()