What is the purpose of ‘use strict’ in JavaScript?

Vaibhav Kothia May 30, 2023 0 Comments

The purpose of “use strict” is to indicate that the code should be executed in “strict mode”. Strict mode is a way to opt in to a restricted variant of JavaScript. Strict mode eliminates some JavaScript silent errors by changing them to throw errors.

For example, in strict mode, assigning a value to a non-writable property will throw an error:

“use strict”;

var obj = {};
Object.defineProperty(obj, “x”, { value: 42, writable: false });

obj.x = 9; // throws an error in strict mode

What is the difference between a function expression and a function declaration?

Vaibhav Kothia May 26, 2023 0 Comments

A function expression is an expression that defines a function. It is usually written as a variable assignment, where a function is assigned to a variable. For example:

const myFunction = function() {
// code here
};

A function declaration is a statement that declares a function. It is written with the function keyword followed by the function name, parameters, and code. For example:

function myFunction() {
// code here
}

What is the purpose of using closures in JavaScript?

Vaibhav Kothia May 26, 2023 0 Comments

Closures are used to create private variables and functions in JavaScript. A closure is a feature in JavaScript where an inner function has access to the outer (enclosing) function’s variables—a scope chain. The closure has three scope chains: it has access to its own scope (variables defined between its curly brackets), it has access to the outer function’s variables, and it has access to the global variables.

Example:

function outerFunction(x) {
let innerVariable = 3;

function innerFunction(y) {
return x + y + innerVariable;
}

return innerFunction;
}

let innerFunc = outerFunction(5);

console.log(innerFunc(2)); // 10

What is the difference between null and undefined in JavaScript?

Vaibhav Kothia May 26, 2023 0 Comments

Null and undefined are two distinct types in JavaScript.

Undefined:
Undefined means a variable has been declared but has not yet been assigned a value.
Example:
let x;
console.log(x); // Output: undefined

Null:
Null is an assignment value. It can be assigned to a variable as a representation of no value.
Example:
let x = null;
console.log(x); // Output: null

What is the use of the ‘this’ keyword in JavaScript?

Vaibhav Kothia May 26, 2023 0 Comments

The ‘this’ keyword in JavaScript is used to refer to the object that the current context belongs to. It can be used to refer to the object that owns the current code or method.

For example:

let person = {
name: ‘John’,
age: 30,
getInfo: function() {
console.log(`Name: ${this.name}, Age: ${this.age}`);
}
};

person.getInfo(); // Outputs: Name: John, Age: 30

What are the different scopes of a variable in JavaScript?

Vaibhav Kothia May 26, 2023 0 Comments

The different scopes of a variable in JavaScript are:

1. Global Scope: A global scope variable is declared outside of any function and can be accessed from any part of the program.

Example:
var x = 10;

2. Local Scope: A local scope variable is declared inside a function and can only be accessed within that function.

Example:
function myFunction() {
var y = 20;
}

3. Block Scope: A block scope variable is declared inside a block statement and can only be accessed within that block statement.

Example:
if (true) {
let z = 30;
}

What are the advantages of using JavaScript?

Vaibhav Kothia May 26, 2023 0 Comments

1. Easy to learn and use: JavaScript is relatively easy to learn and use compared to other programming languages, and it is also widely used, so it is easy to find resources and tutorials for help. For example, if you wanted to make a simple website with a few interactive features, you could easily learn the basics of JavaScript and use it to make your website come to life.

2. Cross-platform compatibility: JavaScript can run on multiple platforms, including web browsers, servers, and mobile devices. This means that you can write code once and it will work on any platform. For example, you could write a JavaScript program that runs on a web browser, and then easily port it to a mobile device with minimal changes.

3. Rich interfaces: JavaScript is used to create interactive web interfaces that make websites more user-friendly and engaging. For example, you could use JavaScript to create drop-down menus, sliders, and other interactive elements that make navigating a website easier.

4. Increased speed: JavaScript can be used to reduce the amount of time it takes for a website to load. For example, you could use JavaScript to pre-load images and other content, so that when a user visits a page, the content is already loaded and ready to go. This can significantly increase the speed of a website.

What is the difference between == and ===?

Vaibhav Kothia May 26, 2023 0 Comments

== is the comparison operator, also known as the “equal to” operator. It checks if the two values on either side of the operator are equal. For example:

let x = 5;
let y = 5;
x == y // returns true

=== is the strict comparison operator, also known as the “equal value and equal type” operator. It checks if the two values on either side of the operator are equal and of the same type. For example:

let x = 5;
let y = ‘5’;
x === y // returns false

What is the difference between call() and apply()?

Vaibhav Kothia May 26, 2023 0 Comments

The main difference between call() and apply() is the way in which arguments are passed to the function.

The call() method takes arguments separately, while the apply() method takes arguments as an array.

Example:

function add(a, b) {
return a + b;
}

// call()
add.call(this, 1, 2); // Output: 3

// apply()
add.apply(this, [1, 2]); // Output: 3

What is the purpose of the void operator?

Vaibhav Kothia May 26, 2023 0 Comments

The void operator is a unary operator that is used to return undefined when evaluated. It is often used to discard the return value of a function.

For example, if you call a function that returns a value, but you do not need that value, you can use the void operator to discard it.

let result = someFunction();
// do something with result

// discard the result
void someFunction();