Javascript 10 Most Important Interview Questions You Need To Know.

JavaScript, also abbreviated as JS, is a high-level server-side programming language. To build a JavaScript programming career, candidates need to crack the interview. They are asked various JavaScript interview questions and answers.

Interview

Q1. “What is JavaScript?”

JavaScript is a scripting language used to create and control dynamic website content, JavaScript was initially created to “make web pages alive”.

The programs in this language are called scripts. They can be written right in a web page’s HTML and run automatically as the page loads.

Scripts are provided and executed as plain text. They don’t need special preparation or compilation to run.

Features like:

• animated graphics
• photo slideshows
• autocomplete text suggestions
• interactive forms

Q2. “What are the data types supported by JavaScript?”

Following are the JavaScript data types supported by JavaScript are:

• Undefined
• Null
• Boolean
• String
• Symbol
• Number
• Object

Q3. “What is Null Vs Undefined function?”

Null is used to represent an intentional absence of value. As we have seen in the variable section that we can assign any primitive or non-primitive type of value to a variable.

What is null?

There are two features of null you should understand:

• null is an empty or non-existent value.
• null must be assigned.

Here’s an example. We assign the value of null to a:

let a = null;console.log(a);
// null

What is undefined?

Undefined most typically means a variable has been declared, but not defined. For example:

let b;console.log(b);
// undefined

null is a special value mean "no value"? null is a special object because typeof null returns 'object'.

On the other hand, undefined means that the variable has not been declared, or has not been given a value.

Q4. “JavaScript — Double Equals vs. Triple Equals?”

Equal to (=) is an assignment operator, == that inherently converts type and === does not convert type.

Double equals

Double equals (==) is a comparison operator, which transforms the operands having the same type before comparison.

An example will illustrate this. Recall earlier when we tested the following with strict equality:

34 === '34'
// false (Number v. String)

Triple Equals

Triple equals (===) is a strict equality comparison operator in JavaScript, which returns false for the values which are not of a similar type.

Let's look at a couple of examples of strict equality.

In this first example, we’re comparing the number 10 with the number 10. As expected, true is returned. Both are numbers, and both share the same value of 10.

10 === 10
// true

Q5. “What is DOM (Document Object Model)?”

The Document Object Model (DOM) is a programming API for HTML and XML documents. DOM stands for Document Object Model. In the world of the web, all HTML web pages are referred to as documents.

The Document Object Model represents each of these web pages in a tree-like structure to make it easier to access and manage the elements.

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