JavaScript filter() Function

The filter() function in JavaScript is an array method used to create a new array with only those elements that pass a test provided by a callback function. It's ideal for selecting a subset of data from an array based on specific conditions.

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What is filter() in JavaScript?

The filter() method goes through each element in an array and includes it in the new array only if the callback function returns true.

✅ The original array remains unchanged.

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Syntax

Parameters:

• currentValue: The current item in the array.
• index (optional): Index of the current item.
• array (optional): The entire array.

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Example 1: Filter Numbers Greater Than a Value

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Example 2: Filter Strings Based on Length

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Example 3: Filtering Array of Objects

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Example 4: Using filter() with Index

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Example 5: Chaining filter() with map()

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Common Use Cases

• Filtering search results in a UI
• Removing null, undefined, or falsy values
• Filtering lists based on user input or permissions
• Processing arrays of objects from APIs or JSON data

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Key Takeaways

• filter() is used to select elements from an array based on a condition.
• It does not modify the original array.
• Returns a new array with only the matching elements.
• Can be combined with map(), reduce(), and other array methods for powerful transformations.