JavaScript Variables: A Beginner's Guide to Storing Data

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In JavaScript, variables are containers for storing data values. They can hold different types of data, such as numbers, strings, objects, arrays, and more.

JavaScript Variables can be declared in 4 ways:

Using var
Using let
Using const

Example (Var)

<!DOCTYPE html>

<html>

<body>

<h1>JavaScript Variables</h1>

<p>In this example, x, y, and z are variables.</p>

var x = 5;

var y = 6;

var z = x + y;

document.getElementById("demo").innerHTML =

"The value of z is: " + z;

</script>

</body>

</html>

Try it yourself

Example (let)

<!DOCTYPE html>

<html>

<body>

<h1>JavaScript Variables</h1>

<p>In this example, x, y, and z are variables.</p>

let x = 5;

let y = 6;

let z = x + y;

document.getElementById("demo").innerHTML =

"The value of z is: " + z;

</script>

</body>

</html>

Try it yourself

Example (const)

<!DOCTYPE html>

<html>

<body>

<h1>JavaScript Variables</h1>

<p>In this example, x, y, and z are variables.</p>

const x = 5;

const y = 6;

const z = x + y;

document.getElementById("demo").innerHTML =

"The value of z is: " + z;

</script>

</body>

</html>

Try it yourself

JavaScript Identifiers

In JavaScript, identifiers are names used to identify variables, functions, arrays, objects, or any other user-defined items. They must follow specific rules to be valid.

The general rules for constructing names for variables (unique identifiers) are:

Must begin with a letter, underscore (_), or dollar sign ($): Names must begin with a letter.

Can contain letters, digits (0-9), underscores (_), or dollar signs ($): after the first character: Names are case sensitive (y and Y are different variables).

Names are case sensitive (y and Y are different variables).

Reserved words (like JavaScript keywords) cannot be used as names.

Note

Some of reserved words are

- break, case, catch, class, const, continue, debugger, default, delete, do, else, export, extends, finally, for, function, if, import, in, instanceof, let, new, return, super, switch, this, throw, try, typeof, var, void, while, with, yield

Examples of Valid and Invalid Identifiers:

1. Valid

let myVar
let _result
let $currency
let age12
let this_is_valid
let café

2. Invalid

let 1number; // Cannot start with a number
let my-var; // Hyphen is not allowed
let let; // "let" is a reserved keyword
let function; // Reserved keyword

Best Practices:

Use meaningful and descriptive names for identifiers to make your code more readable.

Stick to camelCase for variable and function names (myVariableName).

Use uppercase for constants (MAX_VALUE).

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