find-polyfill.html

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<script>
  // https://tc39.github.io/ecma262/#sec-array.prototype.find
  if (!Array.prototype.find) {
    Object.defineProperty(Array.prototype, 'find', {
      value: function(predicate) {
       // 1. Let O be ? ToObject(this value).
        if (this == null) {
          throw new TypeError('"this" is null or not defined');
        }

        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 kValue.
          var kValue = o[k];
          if (predicate.call(thisArg, kValue, k, o)) {
            return kValue;
          }
          // e. Increase k by 1.
          k++;
        }

        // 7. Return undefined.
        return undefined;
      }
    });
  }
  </script>