JavaScript: Variables
Variables are used to store this information.
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.

We can put any value in the box.
We can also change it as many times as we want:
let message;
message = 'Hello!';
message = 'World!'; // value changed
alert(message);
When the value is changed, the old data is removed from the variable:

We can also declare two variables and copy data from one into the other.
let hello = 'Hello world!';
let message;
// copy 'Hello world' from hello into message
message = hello;
// now two variables hold the same data
alert(hello); // Hello world!
alert(message); // Hello world!
let $ = 1; // declared a variable with the name "$"
let _ = 2; // and now a variable with the name "_"
alert($ + _); // 3
Non-Latin letters are allowed, but not recommended
It is possible to use any language, including cyrillic letters or even hieroglyphs, like this:
let имя = '...';
let 我 = '...';
Constants: to declare a constant (unchanging) variable, use const
instead of let
:
const myBirthday = '18.04.1982';
We can declare variables to store data by using the var
, let
, or const
keywords.
let
– is a modern variable declaration. The code must be in strict mode to uselet
in Chrome (V8).var
– is an old-school variable declaration. Normally we don’t use it at all, but we’ll cover subtle differences fromlet
in the chapter The old "var", just in case you need them.const
– is likelet
, but the value of the variable can’t be changed.
Variables should be named in a way that allows us to easily understand what’s inside them.
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