Numbers in JavaScript can be both positive, negative, whole numbers or floats.
Examples of a number:
- 123
- -47
- 0
- 1.45
- -5.33
A Boolean is true or false.
A String is one of more characters wrapped in single or double speechquotes.
Examples of a string:
- 'hello'
- "Goodbye"
- 'a'
- "1"
An Array is a collection of 0 or more elements wrapped in square brackets. In an array you only declare the values
Examples of an array:
- [1, 2, 3]
- ['a', 'b', 'c']
- [1, 2, 'a', 'b']
- []
An Object is also a collection of 0 or more elements wrapped in curly braces. With an Object however, you can name the key as well as the value.
Example of an Object:
{
name: 'Bobbie Dazzler',
age: 20,
male: true,
friends: [ 'Joe', 'Lucy' ]
}
This is a special type for when something has been declared, but no value has been set. It is also used when you try to use something that does not exist.
In terms of undefined vs null, undefined it is what JavaScript itself will set.
In terms of undefined vs null, null it is what YOU will set. JavaScript will never set something to null on its own.
Avoid using it.
Means Not a Number. It is a special type you will not need to use.