JavaScript variables can store many different data types. A "data type" means the type that the data is. For example a person's name is a string data type (text) and their age is a number data type.

let firstName = "Marcus"    // string
let lastName = "Jones"      // string
let age = 17                // number

Strings are written inside double or single quotes. Numbers are written without quotes. If you put a number in quotes, it will be treated as a text string.

let age = "Fifteen" // string
let age = "15"      // string
let age = 15        // number

A string (or a text string) is a series of characters like "Samuel O'Leary". Strings are written with quotes. You can use single or double quotes.

let country1 = "USA"    // double quotes
let country2 = 'Japan'  // single quotes

You can use quotes inside a string, as long as they don't match the quotes surrounding the string.

let sentence1 = "Dave O'Leary";           // Single quote inside double quotes
let sentence2 = "He is called 'Dave'";    // Single quotes inside double quotes
let sentence3 = 'He is called "Dave"';    // Double quotes inside single quotes

In JavaScript numbers can be written with or without decimal points.

let price = 4.99   // a number variable with a decimal point
let age = 23    // a number variable with no decimal point

A boolean is a value that is either true or false. JavaScript booleans can only be one of two values, true or false.

let isWearingHat = true;
let isRaining = false;

Booleans are often used to test conditions in conditional statements such as if then conditional statements.

if (isRaining){
    isWearingHat = true;
}else{
    isWearingHat = false;
}

JavaScript arrays are used to store multiple values in a single variable.

JavaScript arrays are written with square brackets [] and the array items are separated by commas , The following code creates an array called 'team', containing three players.

let team = ["John", "Sarah", "Kyrie"]