JavaScript typeof

Summary: in this tutorial, you’ll learn how to use the JavaScript typeof operator that returns a string representing the type of a value.

Introduction to the JavaScript typeof operator

The typeof operator accepts an operand and returns a string representing the type of the operand. The following shows the syntax of the typeof operator:

typeof(operand)Code language: JavaScript (javascript)

In this syntax, the operand can be a value, a variable, or an expression. Alternatively, you can use the typeof operator without the parentheses like this:

typeof operandCode language: JavaScript (javascript)

Note that if the operand is an expression, you need to use the parentheses to make the syntax valid.

JavaScript typeof examples

The following example shows how to use the typeof operator with values of various types:

let type;

type = typeof 'Hi';
console.log(type); // 'string'

type = typeof 100;
console.log(type); // 'number'

type = typeof 100n;
console.log(type); // 'bigint'

type = typeof false;
console.log(type); // 'boolean'

type = typeof Symbol('morning');
console.log(type); // 'symbol'


type = typeof undefined;
console.log(type); // 'undefined'


type = typeof new Date();
console.log(type); // 'object'Code language: JavaScript (javascript)

In JavaScript, null is a primitive value of the null type. However, its type is not null but object because JavaScript treats null as an empty object:

type = typeof null;
console.log(type); // 'object'Code language: JavaScript (javascript)

Technically, JavaScript treats functions as objects. Therefore, their types are 'object'. However, functions have some special properties, JavaScript needs to differentiate functions and other objects via using a typeof operator. For example:

function add(x, y) {
  return x + y;
}

let type = typeof add;
console.log(type); // 'function';Code language: JavaScript (javascript)

JavaScrippt typeof operator & parentheses

When passing an expression to the typeof operator, you need to use parentheses. For example:

let type = typeof (100 + '10');
console.log(type);Code language: JavaScript (javascript)

Output:

'string'Code language: JavaScript (javascript)

In this example, the expression 100 + '10' returns the string '10010'. Therefore, its type is 'string'. If you don’t use the parentheses, you’ll get an unexpected result. For example:

let type = typeof 100 + '10';
console.log(type);Code language: JavaScript (javascript)

Output:

'number10'Code language: JavaScript (javascript)

In this example, the typeof 100 returns 'number'. Therefore, the result is a string that is the concatenation of the string 'number' and '10'.

Summary

• Use JavaScript typeof operator to get a string that represent the value type.