Array.includes

if (!Array.prototype.includes) {
  Array.prototype.includes = function (element, fromIndex) {
    let len = this.length;
    fromIndex = fromIndex || 0;
    fromIndex = fromIndex >= 0 ? fromIndex : len + fromIndex;
    for (let i = fromIndex; i < len; i++) {
      if (this[i] === element) {
        return true;
      }
    }
    return false;
  };
}