Lesson Weekend

Try this:

> var myNumber = 45;
> myNumber;

myNumber is a variable that we set equal to 45. On the second line, when we type myNumber and press Enter, JavaScript returns the value of the variable. In JavaScript, it's conventional to give variables names that start with a lowercase letter, and if they are more than one word, to capitalize the first letter of subsequent words. This is called lower camel case, because the capitalized letters look like a camel's humps... or something.

Sometimes you'll see a variable initially set without the var keyword, like this:

myNumber = 45;

This works... most of the time, but it can cause really bad bugs down the road. Get in the habit of using the var keyword whenever you create a new variable, and you'll save yourself some massive headaches later.

You can change the value of a variable:

> var myNumber = 45;
> myNumber = 50;
> myNumber;

You can do arithmetic with your variables:

> var favoriteNumber = 13;
> favoriteNumber * 4;

Does the variable change when you perform arithmetic on it?

> var favoriteNumber = 7;
> favoriteNumber + 1;

Nope. But what if we do:

> var favoriteNumber = 6;
>favoriteNumber = favoriteNumber + 1;

Here’s a shortcut: favoriteNumber += 1.

You can use more than one variable at a time, too:

> var num1 = 5;
> var num2 = 6;
> var num3 = num1 + num2;
> num3

Don't worry for the moment about that undefined return value. Technically speaking, it says undefined because declaration of a variable first creates a variable without a value - hence undefined - before assigning it the value that comes to the right of the equals (=) sign.


  • Variable: Variables can be thought of as containers used to store information. They allow for a way to label data with a descriptive name.

  • Lower camel case: Use lowerCamelCase when naming JavaScript variables. Start with a lowercase letter, and if the variable name is more than one word, remove all spaces and capitalize the first letter of each subsequent word.

  • var: Always use the var keyword when initializing variables in JavaScript.


Set a variable equal to a number:

var myNumber = 45;

Use a variable without modifying its value:

favoriteNumber * 4;

Use a variable and modify it:

favoriteNumber = favoriteNumber * 4;


favoriteNumber *= 4;

Use multiple variables:

var myNumber = 45;
var otherNumber = 12;
myNumber + otherNumber;


  • Variables should begin with a letter.

  • Variables are case sensitive (myNumber is a different variable than myNUMBER).

  • Use clear names that describe the value being stored like myNumber.

  • Always name your variables in a manner that will be easy for other developers to understand. Avoid vague letters or initials. (For example: var x = 45 doesn't tell us what the value is. Is 45 an age, a distance, size, a time?...)