JavaScript求解CodeWars缺失数组长度问题遇TypeError报错求助

Hey, I see you're stuck on that TypeError while solving the CodeWars "Length of missing array" problem—let's break down what's going wrong and fix it together.

The Root Cause of Your Error #

The error you're hitting is a classic array boundary issue. Let's look at your loop:

for (let i = 0; i < arr.length; i++) {
    // ...
    else if (arr[i].length - arr[i + 1].length !== 1) {
        // ...
    }
}

When i reaches the last index of your array (i.e., i = arr.length - 1), i + 1 equals arr.length—which is beyond the array's bounds. At that point, arr[i+1] is undefined, so trying to read arr[i+1].length throws the TypeError you're seeing. The console.log you mentioned probably worked for earlier iterations, but the final loop iteration always triggers the error.

Other Issues in Your Code #

Besides the boundary problem, there are a couple of other things that could cause unexpected results:

• You're checking for null/empty subarrays inside the loop, which means you might run several iterations before hitting a null and returning 0. It's better to validate all subarrays upfront.
• Sorting in descending order works, but checking for missing lengths is more intuitive with an ascending sort.

Fixed Code #

Here's a revised version of your function that addresses all these issues:

function getLengthOfMissingArray(arr) {
    // Handle empty or null input immediately
    if (!arr || arr.length === 0) return 0;

    // Check all subarrays for null or empty values first
    for (const subArr of arr) {
        if (!subArr || subArr.length === 0) return 0;
    }

    // Sort subarrays by their length in ascending order
    arr.sort((a, b) => a.length - b.length);

    // Loop through adjacent pairs (stop before the last element)
    for (let i = 0; i < arr.length - 1; i++) {
        // If the next length isn't exactly 1 more than current, we found the missing one
        if (arr[i + 1].length - arr[i].length !== 1) {
            return arr[i].length + 1;
        }
    }

    // If all lengths are consecutive (per problem constraints, this might not be needed, but safe to include)
    return 0;
}

console.log(getLengthOfMissingArray([ [5, 2, 9], [4, 5, 1, 1], [1], [5, 6, 7, 8, 9] ])); // Returns 2, which is correct

Key Fixes Explained #

1. Early Boundary Checks: We first handle null/empty input, then validate every subarray upfront to avoid unexpected errors later.
2. Corrected Loop Boundary: By using i < arr.length - 1, we ensure i + 1 never goes beyond the last valid index of the array—no more undefined errors!
3. Ascending Sort: Sorting from smallest to largest makes it easy to spot the missing length: if the next subarray's length isn't exactly one more than the current, the missing length is current length + 1.
4. Immediate Return: As soon as we find the missing length, we return it directly instead of storing it in a variable, making the code cleaner.

Give this a try—it should resolve your TypeError and correctly solve the problem!

内容的提问来源于stack exchange，提问作者yiw qi