Variables

(var, let, const)

Definition

A variable is a named place to store data so you can use it later.

What Variables Are

Think of a variable as a box with a label:

• The label is the variable name
• The thing inside the box is the value

Shoe Rack Example

If you’re cleaning a room, shoes need a place to go.

• Shoe rack = the variable
• Shoes = the value Later, when you need your shoes, you know exactly where to find them.

Code Example

Step 1: Create a variable (no value yet) let dadsBirthday;

What this means:

• let tells JavaScript: “I’m creating a variable.”
• dadsBirthday is the variable name.
• No value has been placed inside yet, so it’s currently undefined.

Step 2: Store a value in it let dadsBirthday = “June 22, 1998”;

What this means:

• The variable is created AND filled with a value.
• “June 22, 1998” is a string (text in quotes).
• Now whenever you need the birthday, you can use dadsBirthday instead of retyping the date.

Variable Rules

Use let, const, or var

• Correct: let score = 10;

Names must start with a letter, _, or $

• Correct: age, _count, $price
• Incorrect: 1score

No spaces

• Correct: playerScore
• Incorrect: player score

Case matters score and Score are different variables

Use clear names

• Correct: playerLives
• Incorrect: x

Don’t use reserved JavaScript words

• Incorrect: let, if, function

Mini-Quiz

1. What is a variable, in one sentence?
2. Which variable name is valid: 1score or playerScore?