boilerplate.js/Boilerplate/src/js/helpers/pollyfill.js

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// forEach loop for IE 9+ for NodeList
if (window.NodeList && !NodeList.prototype.forEach) {
    NodeList.prototype.forEach = function (callback, thisArg) {
        thisArg = thisArg || window;
        for (var i = 0; i < this.length; i++) {
            callback.call(thisArg, this[i], i, this);
        }
    };
}

if (!Array.prototype.includes) {
    Object.defineProperty(Array.prototype, 'includes', {
        value: function (valueToFind, fromIndex) {

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

            var o = Object(this);

            var len = o.length >>> 0;

            if (len === 0) {
                return false;
            }

            var n = fromIndex | 0;

            var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);

            function sameValueZero(x, y) {
                return x === y || (typeof x === 'number' && typeof y === 'number' && isNaN(x) && isNaN(y));
            }

            while (k < len) {
                if (sameValueZero(o[k], valueToFind)) {
                    return true;
                }
                k++;
            }
            return false;
        }
    });
}