Variables

Programs need to remember values: a user's name, a price, a score in a game. For that, they use variables. A variable is like a box with a label: it has a name, and it holds a value that you can use later.

You create a variable with the keyword let:

let city = "Prague";
console.log(city);

This prints:

Prague

Let's go through the first line:

• let is a keyword, a word with a special meaning in JavaScript. It says that we are creating a new variable.
• city is the name of the variable.
• = stores the value on its right in the variable. In programming, it doesn't mean “equals” as in math; read it as “gets”: city gets the value "Prague".
• "Prague" is the value.

To use the value, write the name of the variable without quotes. console.log(city) prints the value of the variable, Prague, while console.log("city") prints the text city.

A variable can also hold a number, and you can print it together with other values, separated by commas:

let temperature = 18;
console.log("It is", temperature, "degrees outside.");

This prints:

It is 18 degrees outside.

Rules for the names of variables:

• A name can contain letters, digits and the characters _ and $, but it can't start with a digit: price2 is fine, 2price isn't.
• A name can't contain spaces. If it has more words, write them together and start every word after the first one with a capital letter: firstName, priceOfChocolate. This style is called camelCase, because the capital letters stick up like the humps of a camel.
• Uppercase and lowercase letters matter: age and Age are two different variables.
• A name can't be a keyword, such as let.

Choose names that say what the variable holds: price tells you more than p or x.