js simple version map

 

<script>
    var arr = [1, 2,6,9]


    Array.prototype.$map = function (callback) {
      let arr = this
      let ans = new Array()
      for (let i = 0; i < arr.length; i++) {
        ans.push(callback(arr[i]))
      }
      return ans
    }

    var result = arr.$map((item) => {
      return item * 10
    })

    console.log(result);
  </script>