How to replace jQuery.ajax() with vanilla JavaScript in WordPress

In an effort to remove all jQuery dependency from one of my plugins, I decided to turn all jQuery.ajax() requests into vanilla JavaScript requests. Turns out it’s pretty simple.

Here’s the original request, before:

jQuery.ajax({
    type: 'post',
    url: ipAjaxVar.ajaxurl,
    data: 'action=imagepress-like&nonce=' + ipAjaxVar.nonce + '&imagepress_like=&post_id=' + pid,
    success: function (count) {
        if (count.indexOf('already') !== -1) {
            var lecount = count.replace('already', '');
            if (lecount === '0') {
                lecount = ipAjaxVar.likelabel;
            }
            like.removeClass('liked');
            like.html('<svg class="lnr lnr-heart"><use xlink:href="#lnr-heart"></use></svg> ' + lecount);
        } else {
            count = ipAjaxVar.unlikelabel;
            like.addClass('liked');
            like.html('<svg class="lnr lnr-heart"><use xlink:href="#lnr-heart"></use></svg> ' + count);
        }
    }
});

And here’s the vanilla JavaScript request, after:

const request = new XMLHttpRequest();

request.open('POST', ipAjaxVar.ajaxurl, true);
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
request.onload = function () {
    if (this.status >= 200 && this.status < 400) {
        if (this.response.indexOf('already') !== -1) {
            if (this.response.replace('already', '') === '0') {
                likeLabel = ipAjaxVar.likelabel;
            }
            like.classList.remove('liked');
            like.innerHTML = '<svg class="lnr lnr-heart"><use xlink:href="#lnr-heart"></use></svg> ' + likeLabel;
        } else {
            likeLabel = ipAjaxVar.unlikelabel;
            like.classList.add('liked');
            like.innerHTML = '<svg class="lnr lnr-heart"><use xlink:href="#lnr-heart"></use></svg> ' + likeLabel;
        }
    } else {
        // Response error
    }
};
request.onerror = function() {
    // Connection error
};
request.send('action=imagepress-like&nonce=' + ipAjaxVar.nonce + '&imagepress_like=&post_id=' + pid);

Tested and working.