Variables

Most of the time, a JavaScript application needs to work with information. Here are two examples:

An online shop – the information might include goods being sold and a shopping cart. A chat application – the information might include users, messages, and much more. Variables are used to store this information.

A variable A variable is a “named storage” for data. We can use variables to store goodies, visitors, and other data.

To create a variable in JavaScript, use the let keyword.

The statement below creates (in other words: declares) a variable with the name “message”:

let message;

Now, we can put some data into it by using the assignment operator =:

let message;

message = 'Hello'; // store the string 'Hello' in the variable named message

The string is now saved into the memory area associated with the variable. We can access it using the variable name:

let message;
message = 'Hello!';

alert(message); // shows the variable content

To be concise, we can combine the variable declaration and assignment into a single line:

let message = 'Hello!'; // define the variable and assign the value

alert(message); // Hello!

We can also declare multiple variables in one line:

let user = 'John', age = 25, message = 'Hello';

That might seem shorter, but we don’t recommend it. For the sake of better readability, please use a single line per variable.

The multiline variant is a bit longer, but easier to read:

let user = 'John';
let age = 25;
let message = 'Hello';

Some people also define multiple variables in this multiline style:

let user = 'John',
  age = 25,
  message = 'Hello';

…Or even in the “comma-first” style:

let user = 'John'
  , age = 25
  , message = 'Hello';