Array.findIndex()

/**
 * Array.prototype.findIndex() polyfill
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex
 * @license MIT
 */
if (!Array.prototype.findIndex) {
	Object.defineProperty(Array.prototype, 'findIndex', {
		value: function(predicate) {

			if (this == null) {
				throw new TypeError('"this" is null or not defined');
			}

			// 1. Let O be ? ToObject(this value).
			var o = Object(this);

			// 2. Let len be ? ToLength(? Get(O, "length")).
			var len = o.length >>> 0;

			// 3. If IsCallable(predicate) is false, throw a TypeError exception.
			if (typeof predicate !== 'function') {
				throw new TypeError('predicate must be a function');
			}

			// 4. If thisArg was supplied, let T be thisArg; else let T be undefined.
			var thisArg = arguments[1];

			// 5. Let k be 0.
			var k = 0;

			// 6. Repeat, while k < len
			while (k < len) {
				// a. Let Pk be ! ToString(k).
				// b. Let kValue be ? Get(O, Pk).
				// c. Let testResult be ToBoolean(? Call(predicate, T, « kValue, k, O »)).
				// d. If testResult is true, return k.
				var kValue = o[k];
				if (predicate.call(thisArg, kValue, k, o)) {
					return k;
				}
				// e. Increase k by 1.
				k++;
			}

			// 7. Return -1.
			return -1;
		},
		configurable: true,
		writable: true
	});
}