For those times where prefixing is not your cup of tea

unprefix.ts

// Note that unprefixing elements that aren't initially defined will break them
// (which is why it conditionnally unprefixes pointerLockElement)
function unprefix(element:any, prop:string, prefixes:string[]) {
    let capitalized = prop[0].toUpperCase() + prop.substring(1);
    let props = prefixes.map(prefix => prefix + capitalized);
    if (!element[prop]) return Object.defineProperty(element, prop, {
        get: function() {
            for (let prop of props) {
                var val = this[prop];
                if (val) return val;
            }
        },
        set: function(val) {
            props.forEach(prop => this[prop] = val);
        }
    });
    return false;
}
if (unprefix(Element.prototype, 'requestPointerLock', ['moz', 'webkit']))
    unprefix(document, 'pointerLockElement', ['moz', 'webkit']);