Node.replaceChild()

let oldChild = parentNode.replaceChild(newChild, oldChild);

// Given:
// <div>
//  <span id="childSpan">foo bar</span>
// </div>

// Create an empty element node
// without an ID, any attributes, or any content
var sp1 = document.createElement("span");

// Give it an id attribute called 'newSpan'
sp1.id = "newSpan";

// Create some content for the new element.
var sp1_content = document.createTextNode("new replacement span element.");

// Apply that content to the new element
sp1.appendChild(sp1_content);

// Build a reference to the existing node to be replaced
var sp2 = document.getElementById("childSpan");
var parentDiv = sp2.parentNode;

// Replace existing node sp2 with the new span element sp1
parentDiv.replaceChild(sp1, sp2);

// Result:
// <div>
//   <span id="newSpan">new replacement span element.</span>
// </div>