How to use filter function in js

JavaScript filter function is used to filter elements in an array that meet specific conditions and return a new array composed of elements that meet the conditions. Usage includes: filtering elements that meet simple or complex conditions, and creating filter chains. The filter function does not modify the original array. The callback function must return a Boolean value. If a Boolean value is not returned, an error will be thrown.

Usage of filter function in JavaScript

filter The function is a built-in method of JavaScript array. Used to filter elements in an array that meet specific conditions and return a new array consisting of elements that meet the conditions.

Syntax:

<code class="javascript">filter(callback(element, index, array))</code>

Parameters:

• ##callback(element, index, array): A callback function that must return a Boolean value.

  • element: The array element currently being processed.
  • index: The index of the current element in the array.
  • array: The array itself being processed.

Return value:

A new array containing all elements that meet the conditions of the callback function.

Usage:

1. Filter elements that meet simple conditions:

<code class="javascript">const numbers = [1, 2, 3, 4, 5, 6];
const evenNumbers = numbers.filter((num) => num % 2 === 0);</code>

2. Filter elements that meet complex conditions Elements of the condition:

<code class="javascript">const users = [
  { name: 'John', age: 25 },
  { name: 'Mary', age: 30 },
  { name: 'Bob', age: 18 }
];
const adults = users.filter((user) => user.age >= 18);</code>

3. Filter chain:

<code class="javascript">const evenAndGreaterThan3 = numbers.filter((num) => num % 2 === 0).filter((num) => num > 3);</code>

Example:

The following example demonstrates Here's how to use the filter function to filter an array containing student scores to get the list of failed students:

<code class="javascript">const scores = [90, 85, 77, 65, 52, 45];
const failingScores = scores.filter((score) => score < 60);</code>

failingScores The variable will contain the following elements:

52
• 45

Note:

The filter function itself does not modify the original array.
• The callback function must return a Boolean value. If no boolean value is returned, an error will be thrown.

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