JavaScript: Variables

Variables are containers that store values. You start by declaring a variable with the var or the let keyword, followed by the name you give to the variable:

EXAMPLE:

var x = 100;       or let myVariable;

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

1. var is the keyword that tells JavaScript you’re declaring a variable.

2. x is the name of that variable.

3. = is the operator that tells JavaScript a value is coming up next.

4. 100 is the value for the variable to store.

Note: A semicolon at the end of a line indicates where a statement ends.

You can name a variable nearly anything, but there are some restrictions:

• A JavaScript identifier must start with a letter, underscore (_), or dollar sign ($). Subsequent characters can also be digits (0–9).

• Because JavaScript is case sensitive, letters include the characters "A" through "Z" (uppercase) as well as "a" through "z" (lowercase).

EXAMPLE:

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:

EXAMPLE

var total% = 78;

var 2fast2catch = "bold claim";

var function = false;

var class = "easy";

Using variables

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

EXAMPLE:

var y = 200; y + 202;

OutPut

402

You can even use a variable when declaring other variables.

EXAMPLE:

var x = 200; var y = x + 2; y;

OutPut

202

Reassigning variables

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

EXAMPLE:

var weather = "good"; ​weather = "bad"; weather;

OutPut

bad