es6-polyfills.html

<script>
  if (!Array.prototype.find) {
    Object.defineProperty(Array.prototype, 'find', {
      value: function(predicate) {
        'use strict';
        if (this == null) {
          throw new TypeError('Array.prototype.find called on null or undefined');
        }
        if (typeof predicate !== 'function') {
          throw new TypeError('predicate must be a function');
        }
        var list = Object(this);
        var length = list.length >>> 0;
        var thisArg = arguments[1];

        for (var i = 0; i !== length; i++) {
          if (predicate.call(thisArg, this[i], i, list)) {
            return this[i];
          }
        }
        return undefined;
      }
    });
  }

  if (!Array.prototype.findIndex) {
    Object.defineProperty(Array.prototype, 'findIndex', {
      value: function(predicate) {
        if (this == null) {
          throw new TypeError('"this" is null or not defined');
        }

        var o = Object(this);

        var len = o.length >>> 0;

        if (typeof predicate !== 'function') {
          throw new TypeError('predicate must be a function');
        }

        var thisArg = arguments[1];

        var k = 0;

        while (k < len) {
          var kValue = o[k];
          if (predicate.call(thisArg, kValue, k, o)) {
            return k;
          }
          k++;
        }

        return -1;
      }
    });
  }

  if (typeof Object.assign != 'function') {
    // Must be writable: true, enumerable: false, configurable: true
    Object.defineProperty(Object, "assign", {
      // eslint-disable-next-line no-unused-vars
      value: function assign(target, varArgs) { // .length of function is 2
        'use strict';
        if (target == null) { // TypeError if undefined or null
          throw new TypeError('Cannot convert undefined or null to object');
        }

        var to = Object(target);

        for (var index = 1; index < arguments.length; index++) {
          var nextSource = arguments[index];

          if (nextSource != null) { // Skip over if undefined or null
            for (var nextKey in nextSource) {
              // Avoid bugs when hasOwnProperty is shadowed
              if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
                to[nextKey] = nextSource[nextKey];
              }
            }
          }
        }
        return to;
      },
      writable: true,
      configurable: true
    });
  }

  String.prototype.startsWith = String.prototype.startsWith || function(searchString, position){
    position = position || 0;
    return this.substr(position, searchString.length) === searchString;
  };

  String.prototype.endsWith = String.prototype.endsWith || function(searchString, position) {
    var subjectString = this.toString();
    if (typeof position !== 'number' || !isFinite(position) || Math.floor(position) !== position ||
        position > subjectString.length) {
      position = subjectString.length;
    }
    position -= searchString.length;
    var lastIndex = subjectString.lastIndexOf(searchString, position);
    return lastIndex !== -1 && lastIndex === position;
  };

  Array.from = Array.from || (function () {
    var toStr = Object.prototype.toString;
    var isCallable = function (fn) {
      return typeof fn === 'function' || toStr.call(fn) === '[object Function]';
    };
    var toInteger = function (value) {
      var number = Number(value);
      if (isNaN(number)) { return 0; }
      if (number === 0 || !isFinite(number)) { return number; }
      return (number > 0? 1 : -1) * Math.floor(Math.abs(number));
    };
    var maxSafeInteger = Math.pow(2, 53) - 1;
    var toLength = function (value) {
      var len = toInteger(value);
      return Math.min(Math.max(len, 0), maxSafeInteger);
    };

    // The length property of the from method is 1.
    return function from(arrayLike/*, mapFn, thisArg */) {
      // 1. Let C be the this value.
      var C = this;

      // 2. Let items be ToObject(arrayLike).
      var items = Object(arrayLike);

      // 3. ReturnIfAbrupt(items).
      if (arrayLike == null) {
        throw new TypeError("Array.from requires an array-like object - not null or undefined");
      }

      // 4. If mapfn is undefined, then let mapping be false.
      var mapFn = arguments.length > 1? arguments[1] : void undefined;
      var T;
      if (typeof mapFn !== 'undefined') {
        // 5. else
        // 5. a If IsCallable(mapfn) is false, throw a TypeError exception.
        if (!isCallable(mapFn)) {
          throw new TypeError('Array.from: when provided, the second argument must be a function');
        }

        // 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined.
        if (arguments.length > 2) {
          T = arguments[2];
        }
      }

      // 10. Let lenValue be Get(items, "length").
      // 11. Let len be ToLength(lenValue).
      var len = toLength(items.length);

      // 13. If IsConstructor(C) is true, then
      // 13. a. Let A be the result of calling the [[Construct]] internal method
      // of C with an argument list containing the single item len.
      // 14. a. Else, Let A be ArrayCreate(len).
      var A = isCallable(C)? Object(new C(len)) : new Array(len);

      // 16. Let k be 0.
      var k = 0;
      // 17. Repeat, while k < len… (also steps a - h)
      var kValue;
      while (k < len) {
        kValue = items[k];
        if (mapFn) {
          A[k] = typeof T === 'undefined'? mapFn(kValue, k) : mapFn.call(T, kValue, k);
        } else {
          A[k] = kValue;
        }
        k += 1;
      }
      // 18. Let putStatus be Put(A, "length", len, true).
      A.length = len;
      // 20. Return A.
      return A;
    };
  }());

  if (!Element.prototype.matches) {
    Element.prototype.matches = Element.prototype.msMatchesSelector || Element.prototype.webkitMatchesSelector;
  }

  if (!Element.prototype.closest) {
    Element.prototype.closest = function(s) {
      var el = this;
      if (!document.documentElement.contains(el)) {
        return null;
      }
      do {
        if (el.matches(s)) {
          return el;
        }
        el = el.parentElement || el.parentNode;
      } while (el !== null && el.nodeType === 1);
      return null;
    };
  }
</script>