访问回调array.protoype中的参数 [英] accessing arguments in callback array.protoype

问题描述

我正在实现地图功能.要访问我要映射的数组，我根据前面的问题使用了this.现在，我想知道如何访问传递给callback的不同参数.因此，在官方的map方法中，您可以传递索引.我正在尝试执行此操作，但是不确定如何在我的自定义方法中访问它.

I am implementing the map function. To access the array I am mapping over I am using this based on a question I had earlier. Now I am wondering how to access different arguments passed to the callback. So in the official map method you can pass the index. I am trying to do this, but unsure how to access this in my custom method.

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

let x = [1, 12, 3].mapz((item, index) => {
  return item * 2;
})
console.log(x);

推荐答案

您需要将索引作为回调的第二个参数

You need to hand over the index as second parameter for the callback

Array.prototype.mapz = function(callback) {
  const arr = [];
  for (let i = 0; i < this.length; i++) {
    arr.push(callback(this[i], i));
  }
  return arr;
};

let x = [1, 12, 3].mapz((item, index) => {
  console.log(index, item);
  return item * 2;
})
console.log(x);

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