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JavaScript Interview Question

Q. Difference between “ == “ and “ === “ operators.

Ans. Both are comparison operators. The difference between both the operators is that,“==” is used to compare values whereas, “ === “ is used to compare both value and types.

Example -

var x = 2;
var y = "2";
(x == y) // Returns true since the value of both x and y is the same

(x === y) // Returns false since the typeof x is "number" and typeof y is "string"

JavaScript Interview Question

Q. Explain Higher Order Functions in javascript.

Ans. Functions that operate on other functions, either by taking them as arguments or by returning them, are called higher-order functions.

Higher order functions are a result of functions being first-class citizens in javascript.

Examples of higher order functions:

function higherOrder(fn) {
  fn();
}
     
higherOrder(function() { console.log("Hello world") })

function higherOrder2() {
return function() {
return "Do something";
}
}

var x = higherOrder2();
x() // Returns "Do something"

JavaScript Interview Question

Q. What are the advantages and disadvantages of JavaScript?

Ans.
Advantages -
1. Server interaction is less
2. Feedback to the visitors is immediate
3. Interactivity is high
4. Interfaces are richer

Disadvantages -
1. No support for multithreading
2. No support for multiprocessing
3. Reading and writing of files is not allowed
4. No support for networking applications

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JavaScript Interview Question

Q. What is NaN property in JavaScript?

Ans. NaN property represents “Not-a-Number” value. It indicates a value which is not a legal number.

typeof of a NaN will return a Number .

To check if a value is NaN, we use the isNaN() function,

Note- isNaN() function converts the given value to a Number type, and then equates to NaN.

isNaN("Hello")  // Returns true
isNaN(345)   // Returns false
isNaN('1')  // Returns false, since '1' is converted to Number type which results in 0 ( a number) 
isNaN(true) // Returns false, since true converted to Number type results in 1 ( a number)
isNaN(false) // Returns false
isNaN(undefined) // Returns true

JavaScript Interview Question

Q. What is a prototype chain?

Ans. Prototype chaining is used to build new types of objects based on existing ones. It is similar to inheritance in a class based language.

The prototype on object instance is available through
Object.getPrototypeOf(object)
or
proto
property whereas prototype on constructors function is available through
Object.prototype
.

JavaScript Interview Question

Q. What is the significance, and what are the benefits, of including 'use strict' at the beginning of a JavaScript source file?

Ans. The short and most important answer here is that

use strict

is a way to voluntarily enforce stricter parsing and error handling on your JavaScript code at runtime. Code errors that would otherwise have been ignored or would have failed silently will now generate errors or throw exceptions. In general, it is a good practice.

Some of the key benefits of strict mode include:
- Makes debugging easier.
- Prevents accidental globals.
- Eliminates

this

coercion.
- Disallows duplicate parameter values.
- Makes eval() safer.
- Throws error on invalid usage of

delete

.

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JavaScript Interview Question

Q. What are lambda or arrow functions?

Ans. An arrow function is a shorter syntax for a function expression and does not have its own this, arguments, super, or new.target. These functions are best suited for non-method functions, and they cannot be used as constructors.

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