如何在JavaScript中检查函数数组中的函数索引 [英] How to check the index of a function in an Array of functions in JavaScript

问题描述

对于JavaScript，我是一个新的水平。
我有一个函数以 y 作为输入，返回一个大小为 y 的数组，该数组几乎具有与元素具有相同的功能。

I am pretty new level to JavaScript. I have a function taking y as the input to return an array with size y which has almost the same functions as the elements.

这是我的代码：

  function createArrayOfFunctions(y) {
    var arr = [];
    for(var i = 0; i<y; i++) {
    arr[i] = function(x) {    
      return x + i);}  //Probably this is the issue
    }
    return arr;
  }

  var input = "5,3,2";

  var [y, n, m] = input.split(",");
  console.log("input = " + input);
  [y, n, m] = [parseInt(y), parseInt(n), parseInt(m)]
  var addArray = createArrayOfFunctions(y);
  console.log(addArray[n](m));  //I would like to add up n and m

当我执行代码时， i 保持为5，而不是对arr [0]，arr [1]，arr [2]，arr [3]，arr [ 4]。结果，它总是输出 m + y 而不是 n + m 。我尝试使用 indexOF 和 this [i] 来确定函数的索引，但它没有工作。

When I execute the code, the i keeps at 5 instead of iterating from 0,1,2,3,4 for arr[0],arr[1],arr[2],arr[3],arr[4]. As a result, it always output m+y instead of n+m. I have tried to use indexOF and this[i] to figure out the index of the functions, but it does not work. Is there any ways for me to do this?

谢谢！

推荐答案

您遇到了范围界定问题。

You've encountered a scoping issue.

这是一个解决方案：

function createArrayOfFunctions(y) {
  let arr = [];
  for (let i = 0; i < y; i++) {
    arr[i] = function(x) {
      return x + i;
    };
  }
  return arr;
}

以上使用 let ，它将 i 变量的范围限制为每次循环迭代。

The above uses let, which scopes the i variable to each loop iteration.

如果您不能使用 let 由于兼容性，请为每个循环使用IIFE：

If you can't use let due to compatibility, use an IIFE for each loop:

function createArrayOfFunctions(y) {
  var arr = [];
  for (var i = 0; i < y; i++) {
    (function() {
        var _i = i;
        arr[_i] = function(x) {
          return x + _i;
        };
    })();
  }
  return arr;
}

以上代码缓存每个 i IIFE中每个循环的变量，使其保持作用范围。

The above code caches each i variable for each loop in an IIFE, which keeps it in scope.

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