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Convenient type-checking in JavaScript


Convenient high-performance type-checking for JavaScript

value is designed to ease type-checking in JavaScript while keeping performance in mind. It comes with a fluent api to improve the readability of your code. Use value to sanitize function parameters and to provide better error messages if some type is unexpected.

Build Status Dependency Status


npm install value

If you're not using a CommonJS-system in the browser value is namespaced under window.jhnns.value.


var value = require("value");
// value takes every possible type in JavaScript 
// and provides some methods to test for the type. 
value(undefined).typeOf(Object); // = false 
value(null).typeOf(Object); // = false 
value([]).typeOf(Array); // = true 
value([]).typeOf(Object); // = false 
value(2).typeOf(Number); // = true 
value(new String("hello")).typeOf(String); // = true 
value(new String("hello")).typeOf(Object); // = false 
value(/myRegExp/).typeOf(RegExp); // = true 
value(document.createElement("a")).typeOf(HTMLAnchorElement); // = true 
// value also provides a negation for better readability 
value(2).notTypeOf(String); // = true 
// you can also check conveniently for null and undefined with one call 
value(undefined).isSet(); // = false 
value(null).isNotSet(); // = true 
// value also supports convenient type-checking within collections 
value([1, 2, 3]).each.typeOf(Number); // = true 
value([1, "2", 3]).any.notTypeOf(Number); // = true 
value({ one: 1, two: 2, three: null }).any.isNotSet(); // = true 


typeOf(constructor): Boolean Alias: instanceOf

Tests if the subject is a child of the constructor. Respects the complete inheritance chain. Keep in mind that everything that is neither null nor undefined is a child of Object (see below).

notTypeOf(constructor): Boolean Alias: notInstanceOf

Negation of typeOf()

isSet(): Boolean

Returns true when the subject is neither null nor undefined

isNotSet(): Boolean

Negation of isSet()

each.typeOf(constructor): Boolean Alias: each.instanceOf

Invokes value(item).typeOf(constructor) on every item within the given collection. Returns true if every item returned true. A collection can be an array or an object.

each.isSet(): Boolean

Invokes the value(item).isSet() on every item within the given collection. Returns true if every item returned true. A collection can be an array or an object.

any.notTypeOf(constructor): Boolean Alias: any.notInstanceOf

Negation of each.typeOf()

any.isNotSet(): Boolean

Negation of each.isSet()

getConstructor(): Function|null

Returns subject.constructor or null if the subject was null or undefined.


value contains a set of opinionated presumptions to avoid common and annoying pitfalls. It has been designed to act like you would expect from a language like ActionScript with optional static types. The returned result is not always conform with the JavaScript type-specification.

This is a collection of cases where value acts differently to the original typeof-operator:

null is not an Object

In contrast to typeof null === "object"

value(null).typeOf(Object); // = false 

new String() is a String and not an Object

In constrast to typeof new String() === "object"

value(new String()).typeOf(String); // = true  
value(new String()).typeOf(Object); // = false  

[] is an Array and not an Object

In constrast to typeof [] === "object"

value([]).typeOf(Object); // = false 
value([]).typeOf(Array); // = true 

Infinity and NaN are not numbers

In constrast to typeof NaN === "number" and typeof Infinity === "number"

value(NaN).typeOf(Number); // = false 
value(Infinity).typeOf(Number); // = false 

While NaN and Infinity are numbers from a theoretical point of view it's a common mistake when trying to sanitize calculation parameters. value assumes that numbers are numeric - that's why NaN and Infinity are not numbers.

Please note

arguments !== Array

This stays the same: value(arguments).typeOf(Array) will return false because arguments doesn't provide all methods of Array.