# TypeOf Operator
The **`typeof`** operator returns a string indicating the type of the operand's value.
The following table summarizes the possible return values of `typeof`. For more information about types and primitives, see also the [JavaScript data structure](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures) page.
| Type | Result |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------- |
| [Undefined](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined) | `"undefined"` |
| [Null](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/null) | `"object"` ([reason](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof#typeof_null)) |
| [Boolean](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean) | `"boolean"` |
| [Number](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number) | `"number"` |
| [BigInt](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt) | `"bigint"` |
| [String](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String) | `"string"` |
| [Symbol](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol) | `"symbol"` |
| [Function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function) (implements \[\[Call]] in ECMA-262 terms; [classes](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/class) are functions as well) | `"function"` |
| Any other object | `"object"` |
This list of values is exhaustive. No spec-compliant engines are reported to produce (or had historically produced) values other than those listed.
#### [Basic usage](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof#basic_usage)
```
// Numbers
typeof 37 === "number";
typeof 3.14 === "number";
typeof 42 === "number";
typeof Math.LN2 === "number";
typeof Infinity === "number";
typeof NaN === "number"; // Despite being "Not-A-Number"
typeof Number("1") === "number"; // Number tries to parse things into numbers
typeof Number("shoe") === "number"; // including values that cannot be type coerced to a number
typeof 42n === "bigint";
// Strings
typeof "" === "string";
typeof "bla" === "string";
typeof `template literal` === "string";
typeof "1" === "string"; // note that a number within a string is still typeof string
typeof typeof 1 === "string"; // typeof always returns a string
typeof String(1) === "string"; // String converts anything into a string, safer than toString
// Booleans
typeof true === "boolean";
typeof false === "boolean";
typeof Boolean(1) === "boolean"; // Boolean() will convert values based on if they're truthy or falsy
typeof !!1 === "boolean"; // two calls of the ! (logical NOT) operator are equivalent to Boolean()
// Symbols
typeof Symbol() === "symbol";
typeof Symbol("foo") === "symbol";
typeof Symbol.iterator === "symbol";
// Undefined
typeof undefined === "undefined";
typeof declaredButUndefinedVariable === "undefined";
typeof undeclaredVariable === "undefined";
// Objects
typeof { a: 1 } === "object";
// use Array.isArray or Object.prototype.toString.call
// to differentiate regular objects from arrays
typeof [1, 2, 4] === "object";
typeof new Date() === "object";
typeof /regex/ === "object";
// The following are confusing, dangerous, and wasteful. Avoid them.
typeof new Boolean(true) === "object";
typeof new Number(1) === "object";
typeof new String("abc") === "object";
// Functions
typeof function () {} === "function";
typeof class C {} === "function";
typeof Math.sin === "function";
```
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#### [typeof null](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof#typeof_null)
```
// This stands since the beginning of JavaScript
typeof null === "object";
```
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In the first implementation of JavaScript, JavaScript values were represented as a type tag and a value. The type tag for objects was `0`. `null` was represented as the NULL pointer (`0x00` in most platforms). Consequently, `null` had `0` as type tag, hence the `typeof` return value `"object"`. ([reference](https://2ality.com/2013/10/typeof-null.html))
A fix was proposed for ECMAScript (via an opt-in), but [was rejected](https://web.archive.org/web/20160331031419/http://wiki.ecmascript.org:80/doku.php?id=harmony:typeof_null). It would have resulted in `typeof null === "null"`.
#### [Using new operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof#using_new_operator)
All constructor functions called with [`new`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new) will return non-primitives (`"object"` or `"function"`). Most return objects, with the notable exception being [`Function`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function), which returns a function.
```
const str = new String("String");
const num = new Number(100);
typeof str; // "object"
typeof num; // "object"
const func = new Function();
typeof func; // "function"
```