Troubleshooting array.reverse() Issue in *ngFor in Production
Tags: html, arrays, angular, typescript
Published: 2023-08-31 18:59:11

Have you ever encountered a strange issue with the `array.reverse()` method while using it in an `*ngFor` loop in production? Don't worry; you're not alone! In this article, we will dive into the depths of this peculiar problem and explore some possible solutions.

Understanding the Problem
-------------------------

When working with Angular and using the `*ngFor` directive to iterate over an array, you might want to reverse the order of the items for some reason. That's when you decide to use the handy `array.reverse()` method. Everything seems fine during development, but as soon as you deploy your application to production, chaos ensues!

The issue arises because the `array.reverse()` method mutates the original array, causing unexpected behavior in the `*ngFor` loop. In development, this might not be noticeable due to the way Angular handles change detection, but in production, it can lead to strange bugs and even crashes.

Fixing the Issue
----------------

Now that we understand the problem, let's explore some possible solutions:

### 1\. Use a Copy of the Array

One way to avoid the `array.reverse()` issue is to create a copy of the array before reversing it. This can be done using the spread operator or the `Array.slice()` method. By working with a copy, you prevent the original array from being mutated, ensuring the `*ngFor` loop behaves as expected.

 

    
        const reversedArray = [...originalArray].reverse();
        // or
        const reversedArray = originalArray.slice().reverse();
      

 

### 2\. Reverse the Array in the Component

Another approach is to reverse the array in the component itself, rather than within the template. By doing so, you can avoid the `array.reverse()` method altogether. You can use `Array.reverse()` in the component's TypeScript code and then bind the reversed array to the template.

 

    
        // Component code
        reversedArray: any[] = originalArray.reverse();
    
        // Template code
        <div *ngFor="let item of reversedArray">
          
    </div>
  

 

Conclusion
----------

The `array.reverse()` issue in an `*ngFor` loop can be a frustrating problem to encounter in production. However, by understanding the problem and using one of the suggested solutions, you can overcome this issue and keep your application running smoothly. Remember to always test your code thoroughly and have a good laugh when you come across these funny quirks in software development!

References
----------

*   [Angular NgForOf Documentation](https://angular.io/api/common/NgForOf)
*   [MDN Web Docs: Array.reverse()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reverse)

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