onmouseover change image in javascript code example

Example 1: javascript onmouseover change image

let img = document.querySelector('img');
    let start = img.src;
    let hover = img.getAttribute('data-hover'); //specified in img tag

    img.onmouseover = () => { img.src = hover; }
    img.onmouseout = () => { img.src = start; } //to revert back to start

Example 2: how to change image on mouse click in javascript

<img src="imageName1.jpg" onmouseover="imagefun()" id="getImage">