手写js的map与forEach方法

  /* 手写map方法 */
    Array.prototype.myMap = function (fn, thisArg) {
      if (typeof fn !== 'function') {
        throw new Error(`${fn} is not function`)
      }
      let arr = this;
      let newArray = [];
      for (let i = 0; i < arr.length; i++) {
        newArray[i] = fn.call(thisArg, arr[i], i, arr)
      }
      return newArray
    }



    /* 手写forEach */
    Array.prototype.myForEach = function (fun, thisArg) {
      if (typeof fun !== 'function') {
        return new Error('params error')
      }
      if (!Array.isArray(this)) {
        return `${this} is not array`
      }
      let oldArr = this;
      for (var k = 0; k < oldArr.length; k++) {
        console.log(thisArg)
        fun.call(thisArg, oldArr[k], k, oldArr)
      }
    }

    let arr = [1, 2, 3, 4]
    let res = arr.myForEach((item, index) => { return arr[index] = item * 2 })
    console.log(arr)