Question

In another question answered here I found the following JavaScript code:

function _dom_trackActiveElement(evt) {
    if (evt && evt.target) { 
        document.activeElement = evt.target == document ? null : evt.target;
    }
}

But this syntax is unknown to me, could someone explain exactly what

document.activeElement = evt.target == document ? null : evt.target;

does?

Answer 1

? : is the conditional operator, sometimes called the “ternary operator”. As an example, a ? b : c will return b if a is true, and c otherwise.

Your code will assign null to document.activeElement if evt.target == document. Otherwise, evt.target will be assigned.