JavaScript Interview Prep: map(), filter() and reduce()

In Javascript, the map(), filter() and reduce() methods are powerful array functions that allow you to transform and filter arrays easily. They are all higher order functions becaues they take user-defined functions as parameters.

JavaScript Array Map()

• The map() method in JavaScript is used to create a new array by applying a given function to each element of the original array.

const numbers = [5, 10, 15, 20, 25, 30]; 
  
const multipliedNumbers =  
    numbers.map(num => num * 3); 
console.log(multipliedNumbers)

//output: [ 15, 30, 45, 60, 75, 90 ]

• map() creates a new array with the same length as the original array, but with each element transformed by the callback function
• map() is used when you want to transform each element in an array
• map() returns a new array with the same length as the original array

JavaScript Array Filter()

• filter() is used to create a new array that includes only the elements from an existing array that pass a specified condition

const numbers = [5, 10, 15, 20, 25, 30]; 
  
const numbersGreaterThan20 =  
    numbers.filter(num => num > 20); 
  
console.log(numbersGreaterThan20)…