如何在JavaScript中使用带有for循环的嵌套数组 [英] How to use nested arrays with a for loop in javascript

问题描述

我的目标是能够在for循环中访问嵌套数组的属性，例如给定数组.

My goal for this is to be able to access properties of a nested array in a for loop, for example given the array.

[[1 , "one"],
[0.2 , "two"],
[0.3 , "three"]]

我希望能够通过循环访问索引0.

I'd like to be able to access index 0 over a loop.

我目前的做法是:

function printArray() {
  for (var i = arguments.length; i >= 0; i--) {
    print(arguments[i][0]);
  }
}

这怎么会产生此错误

Uncaught TypeError: Cannot read property '0' of undefined

当我期望

0.3
0.2
1

循环遍历嵌套数组的正确方法是什么?

What is the correct way of looping over a nested array?

推荐答案

有两种方法可以遍历数组.

There are a couple of ways to loop through an array.

哪个是最好的?

这取决于它的用途和主观性.

It depends on what it's used for, and subjectivity.

这里有几个.

let arr = [[1 , "one"], [0.2 , "two"], [0.3 , "three"]];

// forEach loop
console.log('forEach loop');
arr.forEach((x, idx) => {
    console.log(x[0]);
});

//for of loop
console.log('for-of loop');
for (elem of arr){
   console.log(elem[0]);
}

//for in loop
console.log('for-in loop');
for (idx in arr){
    console.log(arr[idx][0]);
}

// old-school for loop
console.log('for loop');
for (let i = 0; i < arr.length; i++) { 
    console.log(arr[i][0]); 
}

// while loop
console.log('while loop');
let i = 0;
while (i < arr.length) {
    console.log(arr[i][0]);
    i++;
}

// do while loop
console.log('do while loop');
let j = 0;
do {
    console.log(arr[j][0]);
    j++;
} while (j < arr.length);

但是关于您的功能.
1)最好将数组作为变量传递.
2)数组的最后一个索引是它的长度-1

But about your function.
1) it's better to pass the array as a variable.
2) the last index of an array is it's length - 1

因此，如果您希望某些功能在较旧的浏览器中也可以使用.

So if you want something that even works in older browsers.

以索引的升序循环:

function printArray(arr) {
  for (var i = 0; i < arr.length; i++) {
    print(arr[i][0]);
  }
}

以索引的降序循环:

function printArray(arr) {
  for (var i = arr.length - 1; i >= 0; i--) {
    print(arr[i][0]);
  }
}

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