plain javascript code to highlight an html element

element.style.backgroundColor = "#FDFF47";

#FDFF47 is a nice shade of yellow that seems perfect for highlighting.

Edit for clarification: You're over-complicating things. If you ever want to restore the previous background color, just store element.style.backgroundColor and access it later.

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If for some reason you need to use javascript here is function that temporary highlits element background

function highlight(element) {
    let defaultBG = element.style.backgroundColor;
    let defaultTransition = element.style.transition;

    element.style.transition = "background 1s";
    element.style.backgroundColor = "#FDFF47";

    setTimeout(function()
    {
        element.style.backgroundColor = defaultBG;
        setTimeout(function() {
            element.style.transition = defaultTransition;
        }, 1000);
    }, 1000);
}

If you're debugging in a browser that supports the CSS outline, one simple solution is this:

myElement.style.outline = '#f00 solid 2px';

Old post, but worth adding since it shows up in searches on the topic. A simple way to achieve a highlighting effect is:

myElement.style.filter = "brightness(125%)";