Node.insertBefore()

The Node.insertBefore() method inserts a node before the reference node as a child of a specified parent node. If the given child is a reference to an existing node in the document, insertBefore() moves it from its current position to the new position (there is no requirement to remove the node from its parent node before appending it to some other node).

This means that a node can't be in two points of the document simultaneously. So if the node already has a parent, the node is first removed, then inserted at the new position. The Node.cloneNode() can be used to make a copy of the node before appending it under the new parent. Note that the copies made with cloneNode() will not be automatically kept in sync.

If the reference node is null, the specified node is added to the end of the list of children of the specified parent node.

If the given child is a DocumentFragment, the entire contents of the DocumentFragment are moved into the child list of the specified parent node.

Syntax

var insertedNode = parentNode.insertBefore(newNode, referenceNode);

• insertedNode The node being inserted, that is newNode
• parentNode The parent of the newly inserted node.
• newNode The node to be inserted.
• referenceNode The node before which newNode is inserted.

If referenceNode is null, the newNode is inserted at the end of the list of child nodes.

Return value

The returned value is the added child except when newNode is a DocumentFragment, in which case the empty DocumentFragment is returned.

Example

Example 1

<div id="parentElement">
   <span id="childElement">foo bar</span>
</div>

<script>
// Create the new node to insert
var newNode = document.createElement("span");

// Get a reference to the parent node
var parentDiv = document.getElementById("childElement").parentNode;

// Begin test case [ 1 ] : Exist a childElement --> All working correctly
var sp2 = document.getElementById("childElement");
parentDiv.insertBefore(newNode, sp2);
// End test case [ 1 ]

// Begin test case [ 2 ] : childElement is of Type undefined 
var sp2 = undefined; // Not exist a node of id "childElement"
parentDiv.insertBefore(newNode, sp2); // Implicit dynamic cast to type Node
// End test case [ 2 ]

// Begin test case [ 3 ] : childElement is of Type "undefined" ( string )
var sp2 = "undefined"; // Not exist a node of id "childElement"
parentDiv.insertBefore(newNode, sp2); // Generate "Type Error: Invalid Argument" 
// End test case [ 3 ]
</script>

Example 2

<div id="parentElement">
  <span id="childElement">foo bar</span>
</div>

<script>
// Create a new, plain <span> element
var sp1 = document.createElement("span");

// Get a reference to the element, before we want to insert the element
var sp2 = document.getElementById("childElement");
// Get a reference to the parent element
var parentDiv = sp2.parentNode;

// Insert the new element into the DOM before sp2
parentDiv.insertBefore(sp1, sp2);
</script>

There is no insertAfter() method. It can be emulated by combining the insertBefore method with Node.nextSibling.

In the previous example, sp1 could be inserted after sp2 using:

parentDiv.insertBefore(sp1, sp2.nextSibling);

If sp2 does not have a next sibling, then it must be the last child — sp2.nextSibling returns null, and sp1 is inserted at the end of the child node list (immediately after sp2).

Example 3

Insert an element before the first child element, using the firstChild property.

// Get a reference to the element in which we want to insert a new node
var parentElement = document.getElementById('parentElement');
// Get a reference to the first child
var theFirstChild = parentElement.firstChild;

// Create a new element
var newElement = document.createElement("div");

// Insert the new element before the first child
parentElement.insertBefore(newElement, theFirstChild);

When the element does not have a first child, then firstChild is null. The element is still appended to the parent, after the last child. Since the parent element did not have a first child, it did not have a last child either. Consequently, the new element is the only element, after insertion.

Browser compatibility

Specifications

See also

• Node.removeChild()
• Node.replaceChild()
• Node.appendChild()
• Node.hasChildNodes()
• Element.insertAdjacentElement()
• ParentNode.prepend()