Skip to main content

Javascript interview questions set 3

 


For set 2 please refer to the Javascript interview question set 2.

Let's begin with set 3,

5)Different Array methods?

a)Array map() Method?
.map() It is used when you want to transform elements in an array.
The map() method creates a new array with the results of calling a function for every array element.

The map() method calls the provided function once for each element in an array, in order.

Note: this method does not change the original array.
Ex:var numbers = [65, 44, 12, 4];
var newarray = numbers.map(myFunction)

function myFunction(num) {
  return num * 10;
}


b)When to use the filter method?
.filter()  when you want to select a subset of multiple elements from an array.
The filter() method creates an array filled with all array elements that pass a test (provided as a function).
Note: filter() does not change the original array.
Ex:
var ages = [32, 33, 16, 40];

function checkAdult(age) {
  return age >= 18;
}
ages.filter(checkAdult);


c)When to use find()?
.find() When you want to select a single element from an array.
The find() method returns the value of the first element in an array that pass a test (provided as a function).
Note: find() does not change the original array.

Ex:
var ages = [3, 10, 18, 20];

function checkAdult(age) {
  return age >= 18;
}
ages.find(checkAdult);


d)When to use reduce() and reduceRight()?
.reduce() when you want to derive a single value from multiple elements in an array
The reduce() method reduces the array to a single value.

The reduce() method executes a provided function for each value of the array (from left-to-right).

The return value of the function is stored in an accumulator (result/total).

Note: this method does not change the original array.
Ex:
var numbers = [175, 50, 25];

numbers.reduce(myFunc);

function myFunc(total, num) {
  return total - num;
}

The reduceRight() method reduces the array to a single value.

The reduceRight() method executes a provided function for each value of the array (from right-to-left).

The return value of the function is stored in an accumulator (result/total).
var numbers = [175, 50, 25];

numbers.reduceRight(myFunc);

function myFunc(total, num) {
  return total - num;
}

e)When to use every()?
The every() method checks if all elements in an array pass a test (provided as a function).

The every() method executes the function once for each element present in the array:

If it finds an array element where the function returns a false value, every() returns false (and does not check the remaining values)
If no false occur, every() returns true
Note: every() does not change the original array
Ex:
var ages = [32, 33, 16, 40];

function checkAdult(age) {
  return age >= 18;
}
ages.every(checkAdult);

f)Difference between for loop and forEach loop?
When using the .forEach() you pass an individual function with it’s own scope.
In a for loop you’re polluting whatever scope you place the loop in.
Ex of forEach:
var array = [1,2,3];
array.forEach(function(i){
  console.log(i);
});



I hope you like this article. Please stay connected for set 4.

You can also follow me on Twitter or Linkedin for the latest updates.

Written By:

Saurabh Joshi

Comments

Post a Comment

Popular posts from this blog

Coding Interview Questions Set 1

From this article, I will be sharing with you all a series of articles on coding interview questions. So please stay connected for the latest set of questions. It will be a good brainstorming exercise and will also prepare you for coding interviews and will definitely boost your confidence. So let's start, 1)Reverse of a string with only O(1) extra memory. Solution: var reverse = function(string) {     let result = ''     for(let i= string.length -1; i >= 0; i--){         result += string[i];     }     return result; }; 2)Fizz Buzz: Write a program that will accept a number n and will output number till n but for multiples of three it should output “Fizz” instead of the number and for the multiples of five output “Buzz”. For numbers which are multiples of both three and five output “FizzBuzz”. Solution: var fizzBuzz= function(n) {     const arr=[]     for(i=1; i<=n; i++){ ...
9 comments
Read more

JavaScript: Debouncing | Flipkart UI Interview Question.

To understand this programming practice will go with a quick example. We all do online shopping and we do search for products on Flipkart on the search bar. So when we type on search bar i.e on every keypress we are actually giving API requests to the server, which in response gives us suggestions. Actually, it's a time-consuming task and may degrade the performance of the webpage. So to improve the performance we use debounce function which actually acts as a controller which reduces the API request to the server on keypress event. In simple terms, we are giving API request only after a certain amount of time between two keypress events. A debounce is a higher-order function. Higher-order function: A function that returns another function. Let's dive deep: HTML Code: <input type="text" onkeyup="searchProducts()"/> Consider this as a search bar for Flipkart. On any keypress, we are calling searchProducts() function. Javascri...
Post a Comment
Read more

Node.js: Bundling your Node.js application to single executable for Windows.

In this article, we will see how to bundle Node.js application to a single executable for Windows. What's the need? Well recently, I had taken a work where I needed to convert pdf's(Of similar format) to excel sheet. So I was reading the pdf's from a folder in desktop and I was storing the output excel sheet into a separate folder on the desktop. I used Node.js for the program. Now the client wanted it to install the program on 25 windows machine and his budget was really low. So it was also not possible for me to install node.js for 25 machines and then install the required dependency for each one. One of the solution: While I was searching for an easy solution I found this amazing npm module pkg . This module can make your node.js app work like plug and play type. No need to install Node.js on the client machine or any other dependency.  It helps to make a commercial or trial version of your node.js application without exposing the source code. I found ...
Post a Comment
Read more