How to declare and assign values to variables in JavaScript

JavaScript is a lightweight, interpreted language because of its simplicity. Interpreters typically execute it in web browsers or server-side platforms like Node.js. While JavaScript is interpreted, modern engines can optimize it.

Declaring variables

In JavaScript, we can declare variables using var, let, and const keywords. These keywords are used to declare different kinds of variables. Here is the overview of each kind of keyword:

  • var: It declares a variable globally or locally to an entire function, regardless of block scope.

  • let: It declares block-scoped variables, which are limited to the block, statement, or expression where they are defined.

  • const: It declares a constant (unchangeable) variable. The value must be assigned when the variable is declared and cannot be reassigned.

Note: Read more about the difference between var, let, and const in this Answer.

Assigning variables

We can assign the variable a value using the assignment operator, =. The syntax of declaring and assigning variable a value is:

keyword variable_name = value

Example

The following examples demonstrate how to declare and assign different kinds of variables to the values.

// Using var
var a = 5;
console.log("Value of a:", a);
// Using let
let b = "Hello";
console.log("Value of b:",b);
// Using const
const c = 3.14;
console.log("Value of c:",c);

In the code above:

  • Lines 2–3: It assigns a value, 5, using var and prints the value.

  • Lines 6–7: It assigns b value, Hello, using let and prints the value.

  • Lines 10–11: It assigns c value, 3.14, using const and prints the value.

Declaring multiple values

We can declare and assign multiple values using a single keyword. For example:

let firstName = "User",
    lastName = "1",
    age = 20;
console.log("Values:", firstName, lastName, age);

The code above declares three variables using let and prints them on a single line.

We can declare the variables at the start and assign them values in the middle of the code if we want. For example:

let variable;
console.log("Value:", variable);
variable = "New value";
console.log("Value:", variable);

In the code above, we declare a variable. Its value is undefined at first. When we assign a value, it gets stored in it.

Variable names

The variable names are case-sensitive, meaning that the first letter of a variable name can be uppercase or lowercase and are considered distinct. It’s a common convention in JavaScript to use camelCase for variable names, where the first letter of each word after the first is capitalized. We can use an underscore (_) or dollar sign ($) to start the variable name. Also, spaces are not allowed in variable names. Let’s look at a few examples below:

let $myVariable = "Hey";
let _anotherVariable = 42;
let firstName = "User";
let lastName = "2";
console.log("Value:", $myVariable);
console.log("Value:", _anotherVariable);
console.log("Value:", firstName + " " + lastName);

The code above shows some valid variable names and prints their values to show the validity.

To conclude, variables can be declared and assigned values using keywords like var, let, or const with the assignment operator. By utilizing these declarations effectively, developers can efficiently manage data and control the flow of their programs.

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