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.
typeof Operator
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:
| Output | Input |
|---|---|
| "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 a 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.