Day 17 || Call Back Function || Array Methods in JavaScript || map || filter || reduce || map vs filter vs reduce in JavaScript

JavaScript Topics

Day 17:

• Call Back Function

• Array Methods

• Map(),

• Filter(),

• Reduce()

Call Back Function:

function name(x) {

  console.log("Hema");

  role();

}

function role() {

  console.log("Student");

}

name(role);

let name = (x)=> {

    console.log("Hema");

    role();

  }

 

  let  role = ()=> {

    console.log("Student");

  }

 

  name(role);

Array Methods:

let originalArray = [1, 2, 3, 4, 5];

let newArray = originalArray.map((currValue, ind, arr) => {

//   console.log(currValue * 2);

    return currValue % 2 === 0

});

console.log(newArray);

let originalArray = [1, 2, 3, 4, 5];

let multiply = {

  number: 2,

};

let newArray = originalArray.map(function(currValue, ind, arr) {

//   console.log(currValue * this.number);

  return currValue * this.number;

}, multiply);

console.log(newArray);

let originalArray = [1, 2, 3, 4, 5];

let filterArray = originalArray.filter((currValue, ind, arr) => {

  return currValue % 2 === 0;

});

console.log(filterArray);

let originalArray = [6, 1, 2, 3, 4, 9, 5, 6, 8, 7];

let reduceArray = originalArray.reduce((acc, currValue, ind, arr) => {

    return acc + currValue;

});

console.log(reduceArray);

let originalArray = [1, 2, 3, 4, 5];

let newArray = originalArray.map((currValue, ind, arr) => currValue * 3);

console.log(newArray);

let evenNumber = newArray.filter((currValue) => currValue % 2 === 0);

console.log(evenNumber);

let singleValue = evenNumber.reduce((acc, currValue) => acc + currValue);

console.log(singleValue);

let newArray = originalArray

  .map((currValue, ind, arr) => currValue * 3)

  .filter((currValue) => currValue % 2 === 0)

  .reduce((acc, currValue) => acc + currValue);

console.log(newArray);

Tasks:

Task 1: Call Back

Write a function calculate that takes two numbers and a callback function as arguments. The callback function should perform a mathematical operation (addition, subtraction, multiplication, or division) on the two numbers.

Task 2: Map + Filter

Given an array of words, create a new array that contains the lengths of words that have more than three characters.

const words = ['apple', 'banana', 'pear', 'grape', 'kiwi'];

Task 3: Map + Reduce

Given an array of numbers, create a new array that contains the square of each number and then calculate the sum of the squared values.

const numbers = [1, 2, 3, 4, 5];

Interview Questions:

1. Why are callback functions useful in JavaScript?

2. What is the difference between using map and a for loop for iterating over an array?

3. How does the filter method differ from the map method?

4. Explain the concept of the reduce method in JavaScript?