Content types in variables

Numbers

The content of a variable is of numeric type and operations can be done with these numbers:

• Sum: console.log(3+3)
• Subtraction: console.log(3-3)
• Multiplication: console.log(3*3)
• Division: console.log(3/3)
• Less than: console.log(1<3)
• Greater than: console.log(4>3)
• Greater than or equal: console.log(3 >= 3)
• Less than or equal: console.log(3 <= 3)
• Same in data type and number: console.log(3 === 3)
• Not the same in type and number: console.log(3 === '3')
• Same in number: console.log(3 == 3)
• Not the same: console.log(30 != 20)

String

Content of a variable that consists of the union of characters or text. 

The operations that can be done with a string are:

Join string content using the + symbol, this action is called concatenating text.

For example: 'hello'+'world'

Boolean

It is a data type that only admits true or false values, and it is very useful to check information within any javascript code. 

For example, to check that a user can be logged in, which can be true or false.
We check if one number is greater than another:

console.log(Boolean(5 > 2)); //returns true
console.log(Boolean(3.14)); //returns true
console.log(Boolean('2' === 2)); //returns false
console.log(Boolean('2' == 2)); // returns true
console.log(Boolean(NaN)); // return false
console.log(Boolean(-1)); // Returns false when negative
console.log(Boolean(0)); // Returns false since it is not positive

Undefined

The content type for a variable is undefined, that is, it is an undefined variable or has no value.

Undefined variable example:
console.log(name_var);
var name_var = 5;
This variable is undefined since first you want to show on the screen a variable that has not been defined, so it will not have any value.

Null

The content of a variable is defined and its value is null.

Undefined variable example:
var name_var = null;
console.log(name_var);