Node: insertBefore() method - Web APIs | MDN (original) (raw)

Syntax

insertBefore(newNode, referenceNode)

Parameters

newNode

The node to be inserted.

referenceNode

The node before which newNode is inserted. If this isnull, then newNode is inserted at the end of node's child nodes.

Note: referenceNode is not an optional parameter. You must explicitly pass a Node or null. Failing to provide it or passing invalid values may behave differently in different browser versions.

Return value

Returns the added child (unless newNode is a DocumentFragment, in which case the empty DocumentFragment is returned).

Exceptions

Pre-insert validity

Example

Example 1

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

// Create the new node to insert
const newNode = document.createElement("span");

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

// Begin test case [ 1 ] : Existing childElement (all works correctly)
let sp2 = document.getElementById("childElement");
parentDiv.insertBefore(newNode, sp2);
// End test case [ 1 ]

// Begin test case [ 2 ] : childElement is of Type undefined
sp2 = undefined; // Non-existent 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)
sp2 = "undefined"; // Non-existent node of id "childElement"
parentDiv.insertBefore(newNode, sp2); // Generates "Type Error: Invalid Argument"
// End test case [ 3 ]

Example 2

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

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

// Get the reference element
const sp2 = document.getElementById("childElement");
// Get the parent element
const parentDiv = sp2.parentNode;

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

**Note:**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 thefirstChild property.

// Get the parent element
const parentElement = document.getElementById("parentElement");
// Get the parent's first child
const theFirstChild = parentElement.firstChild;

// Create a new element
const 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 isnull. 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 newly inserted element is the only element.

Specifications

Specification
DOM # dom-node-insertbefore