// create alert div
const alert_box = document.createElement("div")
alert_box.innerText = "Not allowed!";
alert_box.className = "alert";
//get the parrent of where u wanna insert
const cont = document.querySelector(".container");
// get the element you wanna insert before
const prof = document.getElementById("profile");
// do the insert
cont.insertBefore(alert_box, prof);$( "<p>Test</p>" ).insertBefore( ".inner" );// 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)<div id="parentElement">
<span id="childElement">foo bar</span>
</div>
<script>
// Create a new, plain <span> element
let sp1 = document.createElement("span")
// Get the reference element
let sp2 = document.getElementById("childElement")
// Get the parent element
let parentDiv = sp2.parentNode
// Insert the new element into before sp2
parentDiv.insertBefore(sp1, sp2)
</script>
<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>