There are many ways you could do this. Below I've listed two very simple methods. Here I'm assuming you already have a reference to your a element (here I've called this element):

Modifying the href attribute

element.href += '?query=value';

Using a click event listener

element.addEventListener('click', function(event) {

    // Stop the link from redirecting

    event.preventDefault();



    // Redirect instead with JavaScript

    window.location.href = element.href + '?query=value';

}, false);