Vanilla JS loader indicator

loader.js

function Loader(el) {

    el.loader = this;
    this.el = el;
    this.style = document.getElementById('js-loader-styles');
    this.init();

    if (!document.body.animate) {
        if (!this.style) {
            this.style = document.createElement('style');
            this.style.id = 'js-loader-styles';
            this.style.innerText = '@keyframes spinner { 100% { transform: rotate(360deg); } }';
            document.head.appendChild(this.style);
        }
    }
}

Loader.prototype.init = function () {
    if (!this.overlay) {

        this.el.style.position = 'relative';

        this.overlay = document.createElement('div');
        this.overlay.style.display = 'block';
        this.overlay.style.position = 'absolute';
        this.overlay.style.top = 0;
        this.overlay.style.right = 0;
        this.overlay.style.bottom = 0;
        this.overlay.style.left = 0;
        this.overlay.style.backgroundColor = 'rgba(0, 0, 0, 0.2)';

        this.loader = document.createElement('div');
        this.loader.style.position = 'absolute';
        this.loader.style.top = '50%';
        this.loader.style.left = '50%';
        this.loader.style.marginLeft = '-60px';
        this.loader.style.marginTop = '-60px';
        this.loader.style.borderWidth = '1em';
        this.loader.style.borderColor = 'white';
        this.loader.style.borderStyle = 'solid';
        this.loader.style.borderTopColor = 'transparent';
        this.loader.style.borderRadius = '50%';
        this.loader.style.fontSize = '16px';
        this.loader.style.width = '120px';
        this.loader.style.height = '120px';

        if (document.body.animate) {
            this.loader.animate([
                {transform: 'rotate(0deg)'},
                {transform: 'rotate(360deg)'}
            ], {
                duration: 1000,
                iterations: Infinity
            });
        } else {
            this.loader.style.animation = 'spinner 1s linear infinite';
        }

        this.overlay.appendChild(this.loader);
        this.el.appendChild(this.overlay);
    }
};

Loader.prototype.show = function () {
    this.overlay.style.display = 'block';
};

Loader.prototype.hide = function () {
    this.overlay.style.display = 'none';
};

Loader.prototype.destroy = function () {
    if (this.overlay) {
        this.overlay.parentNode.removeChild(this.overlay);
        this.overlay = null;
        this.loader = null;
    }
};