When to Consider Extending Array.prototype Safely in JavaScript?

Dangers of Extending Array.prototype in JavaScript

The Google JavaScript Style Guide cautions against extending Array.prototype. While many believe it's safe to use extensions like Array.prototype.filter = Array.prototype.filter || function(...) {...}, concerns have been raised.

Potential Issues

Extending Array.prototype presents several potential issues:

1. for..in Issues: Extending Array.prototype may disrupt for..in enumeration.
2. Collision with Other Extensions: Multiple libraries or scripts may attempt to extend Array.prototype with conflicting function names.
3. Cross-Browser Compatibility: Shimming standard functionality may not work consistently across all browsers.

Exceptions for Polyfilling

Despite these concerns, extending Array.prototype can be beneficial for polyfilling standard functionality in older browsers. Google's recommendation not to extend Array.prototype likely applies when you're not polyfilling standard methods.

Guidelines for Safe Extension

If you do choose to extend Array.prototype, consider these guidelines:

• Use the extension only when you're confident you're the only one who will extend it with the same function name.
• Test the extension thoroughly in all target browsers.
• Be aware of potential issues with for..in enumeration.

Conclusion

While extending Array.prototype should generally be avoided, it can be a useful technique for polyfilling standard methods, especially when you're certain you're the sole extender. By following the above guidelines, you can mitigate potential risks and ensure the safe use of Array.prototype extensions.

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