Array.prototype.find() Is Undefined

In here it says that this should work: function isPrime(element, index, array) { var start = 2; while (start <= Math.sqrt(element)) { if (element % start++ <

Solution 1:

Use the polyfill instead, just copy-paste the following code (from this link) to enable the find method:

if (!Array.prototype.find) {
  Object.defineProperty(Array.prototype, 'find', {
    enumerable: false,
    configurable: true,
    writable: true,
    value: function(predicate) {
      if (this == null) {
        thrownewTypeError('Array.prototype.find called on null or undefined');
      }
      if (typeof predicate !== 'function') {
        thrownewTypeError('predicate must be a function');
      }
      var list = Object(this);
      var length = list.length >>> 0;
      var thisArg = arguments[1];
      var value;

      for (var i = 0; i < length; i++) {
        if (i in list) {
          value = list[i];
          if (predicate.call(thisArg, value, i, list)) {
            return value;
          }
        }
      }
      returnundefined;
    }
  });
}

Solution 2:

Instead of .find(...), you also can simply use .filter(...)[0]. (For IE >= 9)

Example:

functionisEven(x) {
  return x % 2 == 0;
}
console.log([3, 4, 5].find(isEven)); // 4console.log([3, 4, 5].filter(isEven)[0]); // 4

Reference: Array.prototype.filter()