Answers for "insertbefore method javascript"

js insertbefore

// The Node.insertBefore() method inserts a node before a
// reference node as a child of a specified parent node.
let insertedNode = parentNode.insertBefore(newNode, referenceNode)

insertbefore

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

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

// Get a reference to the parent node
let 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
let 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 )
let sp2 = "undefined" // Non-existent node of id "childElement"
parentDiv.insertBefore(newNode, sp2) // Generates "Type Error: Invalid Argument"
// End test case [ 3 ]
</script>