Variables
Variables are named values and can store any type of JavaScript value.
Here’s how to declare a variable:
EXAMPLE |
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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.
EXAMPLE |
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var x = 100; x + 102; |
OUTPUT |
202 |
You can even use a variable when declaring other variables.
EXAMPLE |
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var x = 100; var y = x + 102; y; |
OUTPUT |
202 |
Reassigning variables
You can give an existing variable a new value at any point after it’s declared.
EXAMPLE |
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var weather = "rainy"; weather = "sunny"; weather; |
OUTPUT |
"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:
EXAMPLE |
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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 |
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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.