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The Node.firstChild read-only property returns the node's first child in the tree, or null if the node has no children. If the node is a Document, it returns the first node in the list of its direct children.

Syntax

var childNode = node.firstChild;

Example

This example demonstrates the use of firstChild and how whitespace nodes might interfere with using this property.

<p id="para-01">
  <span>First span</span>
</p>

<script>
  var p01 = document.getElementById('para-01');
  console.log(p01.firstChild.nodeName);
</script>

In the above, the console will show '#text' because a text node is inserted to maintain the whitespace between the end of the opening <p> and <span> tags. Any whitespace will create a #text node, from a single space to multiple spaces, returns, tabs, and so on.

Another #text node is inserted between the closing </span> and </p>tags.

If this whitespace is removed from the source, the #text nodes are not inserted and the span element becomes the paragraph's first child.

<p id="para-01"><span>First span</span></p>

<script>
  var p01 = document.getElementById('para-01');
  console.log(p01.firstChild.nodeName);
</script>

Now the alert will show 'SPAN'.

To avoid the issue with node.firstChild returning #text or #comment nodes, ParentNode.firstElementChild can be used to return only the first element node. However, node.firstElementChild requires a shim for Internet Explorer 9 and earlier.

Specifications

Specification Status Comment
DOM
The definition of 'Node.firstChild' in that specification.
Living Standard No change
Document Object Model (DOM) Level 3 Core Specification
The definition of 'Node.firstChild' in that specification.
Obsolete No change
Document Object Model (DOM) Level 2 Core Specification
The definition of 'Node.firstChild' in that specification.
Obsolete No change
Document Object Model (DOM) Level 1 Specification
The definition of 'Node.firstChild' in that specification.
Obsolete Initial definition

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support Yes121 Yes Yes Yes
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support Yes Yes ?4 Yes Yes Yes

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 最近更新: fscholz,