There are five simple data types, primitive types, in ECMAScript:
Undefined, Null, Boolean, Number, and String.
There is one complex data type called Object, which is an unordered list of name-value pairs.
Because ECMAScript is loosely typed, there needs to be a way to determine the data type of a given variable.
The typeof operator provides that information. Using the typeof operator on a value returns one of the following strings:
|"undefined"||if the value is undefined|
|"boolean||if the value is a Boolean|
|"string"||if the value is a string|
|"number"||if the value is number|
|"object"||if the value is an object (other than a function) or null|
|"function"||if the value is a function|
The typeof operator is called like this:
var message = "some string"; console.log(typeof message); //"string" console.log(typeof 5); //"number"
In this example, both a variable (message) and a numeric literal are passed into the typeof operator.
typeof is an operator, no parentheses are required.
typeof sometime returns a confusing but technically correct value.
typeof null returns a value of
"object", as the special value null is considered to be an empty object reference.