How to implement a forEach? with native JS

Array.prototype._forEach = function(fn) {
  //  forEach 
};

function Person(age) {
  this.age = age;
  [3,5,10]._forEach(function(it){
      console.log(`${it} year later I"m ${this.age + it} year old`);
  });
}

let mike = new Person(12);
// 3 year later I"m 15 year old
// 5 year later I"m 17 year old
// 10 year later I"m 22 year old
Javascript
Apr.05,2021

your question should be, how to use ES3 to implement the forEach method of ES5 Array? 

// Production steps of ECMA-262, Edition 5, 15.4.4.18
// Reference: http://es5.github.io/-sharpx15.4.4.18
if (!Array.prototype.forEach) {

  Array.prototype.forEach = function(callback, thisArg) {

    var T, k;

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

    // 1. Let O be the result of calling toObject() passing the
    // |this| value as the argument.
    var O = Object(this);

    // 2. Let lenValue be the result of calling the Get() internal
    // method of O with the argument "length".
    // 3. Let len be toUint32(lenValue).
    var len = O.length >>> 0;

    // 4. If isCallable(callback) is false, throw a TypeError exception. 
    // See: http://es5.github.com/-sharpx9.11
    if (typeof callback !== "function") {
      throw new TypeError(callback + ' is not a function');
    }

    // 5. If thisArg was supplied, let T be thisArg; else let
    // T be undefined.
    if (arguments.length > 1) {
      T = thisArg;
    }

    // 6. Let k be 0
    k = 0;

    // 7. Repeat, while k < len
    while (k < len) {

      var kValue;

      // a. Let Pk be ToString(k).
      //    This is implicit for LHS operands of the in operator
      // b. Let kPresent be the result of calling the HasProperty
      //    internal method of O with argument Pk.
      //    This step can be combined with c
      // c. If kPresent is true, then
      if (k in O) {

        // i. Let kValue be the result of calling the Get internal
        // method of O with argument Pk.
        kValue = O[k];

        // ii. Call the Call internal method of callback with T as
        // the this value and argument list containing kValue, k, and O.
        callback.call(T, kValue, k, O);
      }
      // d. Increase k by 1.
      kPP;
    }
    // 8. return undefined
  };
}

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