Here I have added 70+ JavaScript Interview Questions for Freshers to improve their JavaScript skills and JavaScript knowledge.
When we talk about web development then JavaScript is the first language that comes to mind, JavaScript is a trendy and powerful language we can do anything in web development Android development software development by using JavaScript.
Whenever you sit in an interview for a web developer, frontend developer, backend developer, or full stack developer you will face these questions every time. Sometimes you know the concept but you can’t express your knowledge. The most important thing is interviewer doesn’t have that much time to understand your difficulties and reject you when you can’t answer their questions.
So you will get the Best JavaScript Interview Questions for Freshers to get more prepared for your next interview.
Best JavaScript Interview Questions for Freshers
JavaScript is a very popular and powerful language, you can build web apps, software, Android, and IOS apps using JavaScript. JavaScript is everywhere in the form of libraries and frameworks.
We use our script in the form of React for web development and React Native for Android and IOS app development.
Basic JavaScript Interview Questions
let’s jump on JavaScript Interview Questions for Freshers –
What is Var, Let, Const?
Var function scoped variable in JavaScript, Var is present js in the Early Times of JavaScript. We can use Var as a function scope variable, if we try to access Var out of the function scope it throws a reference error.
LET is a block-scoped variable in JavaScript and let is introduced in ES6, if we try to use let out of scope we get a reference error.
Const is also a block-scoped variable in JavaScript, this is also introduced in ES6 JavaScript. We can use Const for constant values, and if we try to access a Const variable out of scope it throws a reference error.
What is Function in JavaScript?
In programming, “functions” are reusable pieces of code that perform a specific task and can be called upon multiple times within a program.
With the help of a function, we can perform calculation tasks and logical actions through JavaScript multiple Times.
What is Block Scope and Function Scope?
Blocks scope variables are just block-defined variables, blocks are just written by curly braces and also blocks are just function bodies.
Block scopes are used in loops and conditional statements.
Function Scope variables are declared within the function, variables declared using “Var” these are functions scoped, and we can use these variables into the function scope but when we try to access these from out of function then they throw a reference error.
What is Hoisting in Javascript?
Hoisting is a default behaviour of JavaScript where JavaScript Moves the variables and function declaration part on the top of the page and when the execution time comes the function and variable access before their actual declaration of code.
Functions are Hoisted –
// Function hoisting
greet(); // Output: "Hello Bhavesh!"
function greet() {
console.log("Hello Bhavesh!");
}“Var” is the only variable that contains the hoisting property of JavaScript –
//Var Variable Hoisting
console.log(user) //undefined
var user = "Bhavesh";Let and Const variables are not hoisted, when we try to access them before their declaration they throw an error “ReferenceError: Cannot access ‘age’ before initialization“.
//Let and Const Variable
console.log(a,b); //Cannot access 'age' before initialization
let a = 10;
const b = 20;How many datatypes are in javascript? (Primitive and Non-Primitive Datatypes)
There are two types of data types present in JavaScript. The first is primitive and the second one is the non-primitive data type.
Primitive data types are further 6 types –
- String
- Number
- Boolean
- Undefined
- Null
- Symbol
let str = "Bhavesh" //String
let num = 20 //Number
let isLogin = true //boolean
let data = undefined //undefined
let data1 = null //nullNon-primitive data types have only one type in JavaScript –
- Object
let obj = {
name:"Bhavesh",
age:22,
email:"contact@bhaveshbishnoi.com"
}What is Closers in JavaScript?
A Closures in JavaScript is the feature where an inner function has access to the outer function variables even after the outer function has finished the execution but Closures maintain and preserves the environment in which they were created.
Closures are used to create private variables, we can’t access these private variables from outside the closer function.
function countFn() {
let count = 0; // `count` is a private variable
return function () {
count++;
console.log(count);
};
}
const increment = countFn();
increment(); // Output: 1
increment(); // Output: 2
increment(); // Output: 3What is IIFE in JavaScript?
IIFE is an immediately invoked function expression in JavaScript, we use IIFE when we want to execute a function immediately without executing it manually.
Code -
(function (){
console.log("Hello World")
})() // Output - "Hello World"Difference b/w “==” and “===” operators?
In JavaScript, == and === are comparison operators used to compare two values. “==” checks only the given value data and compare both values.
But “===” checks the value with their datatypes, if the value is equal but the datatypes don’t match then it returns false.
What are conditional statements in JavaScript?
Conditional statements are where we can write any condition based on that condition, if our condition is true then this piece of code is executed and if our condition is false then another is executed.
let a = 10;
let b = 20;
if(a==b){
console.log("A and B is Equal")
}else{
console.log("A and B is Not Equal")
}
// If a and b is same If conditition is executed else "else" is executed.How many types of loops are in JavaScript?
There are multiple types of loops in JavaScript, we can use these moves as we want or some of these loops used for specific types of data like Array and Objects.
We have six types of basic loops in JavaScript –
For Loop – Used when the number of iterations is known.
for(let i = 0; i<=10;i++){
console.log(i);
}While Loop – Used when the number of iterations is not known.
let i = 0;
while (i < 5) {
console.log(i);
i++;
}Do-While Loop – Similar to while but always executes at least once.
let i = 0;
do {
console.log(i);
i++;
} while (i < 5);For-in Loop – Used for iterating over object properties.
const obj = {a: 1, b: 2, c: 3};
for (const key in obj) {
console.log(key, obj[key]);
}For-of Loop – Used for iterating over iterable objects like arrays.
const array = [1, 2, 3, 4, 5];
for (const value of array) {
console.log(value);
}ForEach Loop – Used for iterating over arrays with a callback function.
const array = [1, 2, 3, 4, 5];
array.forEach((value) => {
console.log(value);
});What is DOM?
DOM stands for Document Object Model. It is a programming interface for web documents. The DOM represents the page so that programs can change the document structure, style, and content.
How we can get DOM Element references in JavaScript?
To manipulate the web page and interact with the web page which JavaScript we can use these Dom integration queries.
We can interact with the web page using a particular element ID, class, and element name.
const element = document.getElementById("myElementId");
const elements = document.getElementsByClassName("myClass");
const elements = document.getElementsByTagName("div");
const element = document.querySelector(".myClass");
const elements = document.querySelectorAll(".myClass");
