The non-abstract class '_RenderSlider Element' is missing implementations for these members: - RenderObject Element.insertChild RenderObject code example

Example 1: 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)

Example 2: js insert before

// 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);