JavaScript Syntax

In this tutorial, you will learn JavaScript syntax. It has basically a set of rules that define how a JavaScript program is written and interpreted by the browser or JavaScript engine.

1. Variables

Used to store data values.

Declared using var, let, or const.


var x = 10;
let y = 20;
const name = "John";

2. Semicolons

It is used to terminate the statement. Semicolons are often optional.


let x = 5;
let y = 10;

3. Automatic Type Conversion (Coercion)

JavaScript automatically converts data types when performing operations between different types (e.g., adding a number to a string).


let result = 5 + "5"; // "55" (number 5 is converted to string)

4. Identifiers

Identifiers are names given to variables, functions, and objects. They must start with a letter, underscore (_), or dollar sign ($), followed by letters, digits, underscores, or dollar signs.


let name = "John";
let $numValue = 100;
let _isUserAllowed = true;

Note: We can’t declare a variable that starts with a number.


let 1name = "John";  // not allowd

5. Reassigning Variables

Variables declared with var or let can be reassigned.

Variables declared with const cannot be reassigned.


let a = 10;
a = 20; // Valid

const b = 50;
// b = 100; // Error: Assignment to constant variable.

JavaScript Syntax – Interview Questions

Q 1: What is JavaScript syntax?

Ans: It is the set of rules used to write JavaScript code.

Q 2: Is JavaScript case-sensitive?

Ans: Yes, JavaScript is case-sensitive.

Q 3: How are statements separated?

Ans: Using semicolons (;).

Q 4: How do you write a JavaScript block?

Ans: Using curly braces { }.

Q 5: How do you declare variables in JavaScript?

Ans: Using var, let, or const.