JavaScript Variables: A Beginner's Guide to Storing Data

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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