Скачать или смотреть Why findIndex Isn't Finding Your First Matching Array Element?

Discover the common mistake that leads to `findIndex` returning -1 instead of the correct index in JavaScript arrays. Learn how to properly use the `findIndex` method for your needs!
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Why findIndex Isn't Finding Your First Matching Array Element?

When working with arrays in JavaScript, the findIndex method can be an incredibly useful tool. However, it's not uncommon for developers to encounter problems when using it. One such problem arises when attempting to locate the index of the first element in an array that meets a certain condition. If you're facing issues with this method returning -1 instead of the expected index, you're not alone.

The Scenario

Let's consider a practical example to understand what's happening. Imagine you have the following JavaScript code:

[[See Video to Reveal this Text or Code Snippet]]

You want to find the index of the first element in the scoreTierMins array that is greater than or equal to pctScore.

You might write:

[[See Video to Reveal this Text or Code Snippet]]

However, you receive a result of -1, which can be quite confusing. Shouldn’t the index of 70 (the first element that meets the condition) be 1?

The Actual Problem

The issue lies in how the function's return value is handled. In the code you supplied, the comparison el >= pctScore does not return a value because there is no return statement. The way your code is currently written, it's equivalent to this:

[[See Video to Reveal this Text or Code Snippet]]

As a result, JavaScript discards the comparison's value, leading to -1 being returned, which indicates that no element was found.

The Solution

To fix this, you'll need to explicitly return the result of your comparison. Here's how you can do it:

[[See Video to Reveal this Text or Code Snippet]]

Using Arrow Functions for Conciseness

If you're familiar with ES6 syntax, you can achieve the same result using an arrow function, making the code more concise:

[[See Video to Reveal this Text or Code Snippet]]

In this approach, when the body of an arrow function contains just one expression (like our comparison), it is implicitly returned, meaning you don’t have to use the return keyword.

Conclusion

In summary, if your findIndex method is returning -1 when you're expecting a valid index, ensure that you are returning the result of your condition within the function. Adding return statements is key for the function to evaluate the comparisons correctly.

Whether you use the traditional function syntax or the more modern arrow function syntax, understanding how to properly return values will allow you to effectively use the findIndex method in your JavaScript code.

Happy coding!