What are Variables?

A variable is like a labeled box that stores a value. You give the box a name, and you can put something inside it.

Creating Variables

Use let and = to store a value in a variable:

javascript

let name = "Alex";

let age = 10;

Output

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If a value never changes, use const instead:

javascript

const birthYear = 2016;

Output

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Types of Values

Strings — text inside quotes:

javascript

let color = "blue";

let greeting = 'Hello!';

Output

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Numbers — whole numbers and decimals:

javascript

let score = 100;

let temperature = 21.5;

Output

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Booleans — true or false (always lowercase in JavaScript!):

javascript

let isHappy = true;

let isRaining = false;

Output

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Naming Variables

JavaScript names are usually written in camelCase: the first word is lowercase, and every next word starts with a capital letter, like myName or highScore. Names can't contain spaces or start with a number.

Using Variables

You can use variables in console.log():

javascript

let name = "Alex";

console.log(name);

Output

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Output:

Alex

You can log variables with text:

javascript

let name = "Alex";

console.log("Hello,", name);

Output

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Output:

Hello, Alex

Changing Variables

You can change what's inside a variable made with let:

javascript

let score = 0;

console.log(score);

score = 100;

console.log(score);

Output

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Output:

0
100

The old value is replaced by the new one. Notice you only write let the first time — after that, just use the name.