Range.setStart() - Web APIs 编辑

The Range.setStart() method sets the start position of a Range.

If the startNode is a Node of type Text, Comment, or CDataSection, then startOffset is the number of characters from the start of startNode. For other Node types, startOffset is the number of child nodes between the start of the startNode.

Setting the start point below (lower in the document) the end point will result in a collapsed range with the start and end points both set to the specified start position.

Syntax

range.setStart(startNode, startOffset);

Parameters

startNode

The Node where the Range should start.

startOffset

An integer greater than or equal to zero representing the offset for the start of the Range from the start of startNode.

Examples

Highlight part of an element

This example uses the Range.setStart() and Range.setEnd() methods to add part of an address to a range. The selected range is then highlighted using  Range.surroundContents().

The address contains nine nodes: five text nodes, and four <br> elements.

HTML

<p id="address">Wyatt Earp<br>
101 E. Main St.<br>
Dodge City, KS<br>
67801<br>
USA</p>

<hr>
<p>Nodes in the original address:</p>
<ol id="log"></ol>

JavaScript

const address = document.getElementById('address');
const log = document.getElementById('log');

// Log info
address.childNodes.forEach(node => {
  const li = document.createElement('li');
  li.textContent = `${node.nodeName}, ${node.nodeValue}`;
  log.appendChild(li);
});

// Highlight the street and city
const startOffset = 2;  // Start at third node: 101 E. Main St.
const endOffset = 5;    // End at fifth node: Dodge City, KS
const range = document.createRange();
range.setStart(address, startOffset);
range.setEnd(address, endOffset);

const mark = document.createElement('mark');
range.surroundContents(mark);

Result

Get characters from a text node

This example uses the Range.setStart() and Range.setEnd() methods to define the contents of a range. The resulting range contains the first through fifth characters within a text node.

HTML

<p id="content">0123456789</p>
<p id="log"></p>

JavaScript

const element = document.getElementById('content');
const textNode = element.childNodes[0];
const range = document.createRange();
range.setStart(textNode, 0);  // Start at first character
range.setEnd(textNode, 5);    // End at fifth character
document.getElementById('log').textContent = range;

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The DOM interfaces index