如何修复JavaScript二维数组冒泡排序的未定义错误？

Let’s break down what’s causing this error and how to fix it. The root issue here is a simple loop boundary mistake—your code is trying to access an element that doesn’t exist when it reaches the end of the array.

Why the Error Happens #

Your for loop uses i < arr.length as its condition. For an array with 4 elements (indices 0 to 3), this means i will run up to 3. When i = 3, i+1 = 4, which is beyond the array’s bounds. arr[4] is undefined, so trying to access undefined[1] throws the "Cannot read property '1' of undefined" error.

The Simple Fix #

Adjust your loop condition to stop one index earlier: use i < arr.length - 1 instead. This ensures i never reaches the last element, so i+1 will always point to a valid element in the array.

Here’s the corrected code:

let unsortedArr = [[1, 7], [2, 5], [3, 4], [4, 10]]
let sorted = false;
function sort(arr){
 while (!sorted) {
  sorted = true;
  // Update loop condition to avoid out-of-bounds access
  for (let i = 0; i < arr.length - 1; i++) {
   if (arr[i][1] > arr[i + 1][1]) {
    sorted = false;
    let temp = arr[i];
    arr[i] = arr[i + 1];
    arr[i + 1] = temp;
   }
  }
 }
 console.log(arr)
}
sort(unsortedArr) // Output: [[3, 4], [2, 5], [1, 7], [4, 10]]

Bonus: Optimize Your Bubble Sort #

If you want to make the algorithm more efficient, you can track the last position where a swap occurred. This lets you avoid looping over already sorted elements at the end of the array:

let unsortedArr = [[1, 7], [2, 5], [3, 4], [4, 10]]
function sort(arr){
 let lastSwapIndex;
 let endIndex = arr.length - 1;
 while (endIndex > 0) {
  lastSwapIndex = 0;
  for (let i = 0; i < endIndex; i++) {
   if (arr[i][1] > arr[i + 1][1]) {
    let temp = arr[i];
    arr[i] = arr[i + 1];
    arr[i + 1] = temp;
    lastSwapIndex = i;
   }
  }
  endIndex = lastSwapIndex;
 }
 console.log(arr)
}
sort(unsortedArr)

This optimized version stops unnecessary iterations once the trailing sorted portion of the array is confirmed.

内容的提问来源于stack exchange，提问作者skywalker