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:

filter(callback(element, index, array))

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:

const numbers = [1, 2, 3, 4, 5, 6];
const evenNumbers = numbers.filter((num) => num % 2 === 0);

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

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

3. Filter chain:

const evenAndGreaterThan3 = numbers.filter((num) => num % 2 === 0).filter((num) => num > 3);

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:

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

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.

The above is the detailed content of How to use filter function in js. For more information, please follow other related articles on the PHP Chinese website!