Variables are named values and can store any type of JavaScript value.

Here’s how to declare a variable:

var x = 100;

And here’s what’s happening in the example above:

  • var is the keyword that tells JavaScript you’re declaring a variable.
  • x is the name of that variable.
  • = is the operator that tells JavaScript a value is coming up next.
  • 100 is the value for the variable to store.

Using variables

After you declare a variable, you can reference it by name elsewhere in your code.

var x = 100;
x + 102;

You can even use a variable when declaring other variables.

var x = 100;
var y = x + 102;

Reassigning variables

You can give an existing variable a new value at any point after it’s declared.

var weather = "rainy";
​weather = "sunny";

Naming variables

Variable names are pretty flexible as long as you follow a few rules:

  • Start them with a letter, underscore _, or dollar sign $.
  • After the first letter, you can use numbers, as well as letters, underscores, or dollar signs.
  • Don’t use any of JavaScript’s reserved keywords.

With that in mind, here are valid variable names:

var camelCase = "lowercase word, then uppercase";
var dinner2Go = "pizza";
var I_AM_HUNGRY = true;
var _Hello_ = "what a nice greeting"
var $_$ = "money eyes";

And here are some invalid variable names — try to spot what’s wrong with each of them:

var total% = 78;
var 2fast2catch = "bold claim";
var function = false;
var class = "easy";

Variable names are case-sensitive, so myVar, MyVar, and myvar are all different variables. But generally, it’s a good practice to avoid naming variables so similarly.

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