TypeOf-In

allows your values to be compared with a set of Constructors or Strings representing the expected type.

Foretaste:

    var typeOf = require('typeof-in'); 
    typeOf('lollipop').In([null, undefined, NaN, Number, Array, Object]) 

Why use TypeOf-In ?

typeof and instanceof are, somehow, broken

null

For example, null has a type of an object, but it is not an instance of Object.

typeof null; // 'object'
null instanceof Object //false

[fun fact] Object.prototype has the same result as null with typeof and instanceof

RegEx

Using a regular expression literal, someone would expect typeof to return a specific value like "regexp" which would be great in a perfect world.

typeof /regularExpression/ // 'object'
/regularExpression/ instanceof RegExp // true

So, if you're dealing with regex, use instanceof.

Primitives x Objects

Unlike RegEx, other values like Number, String or Boolean have some issues when we want to retrieve their type when we use them as primitive or object (wrapper).

typeof new Number(42) //'object' , create an object
typeof Number(42) //'number', create a primitive value
typeof 42 //'number'
 
666 instanceof Number //false
new Number(42) instanceof (666).constructor //true, because:
(666).constructor === Number.prototype.constructor

So, the previous example shows that it is possible to verify a primitive value with typeof and its wrapper with instanceof but we can't test both of them with the same method even if they share the same constructor. One method to deal with this problem would be to use typeof value.valueOf().

NaN

One of the most famous example in JavaScript is NaN (a.K.a "Not a Number") which return a type of: number...

typeof NaN //'number' *sigh*
typeof new Number(NaN) //'object' *sigh* x 2

Prototypes

As you may have noticed above, prototypes have a weird behavior. For example, the prototype of an Array is an empty Array, and it is the same thing with Number, String, Boolean... which store a default value (0,"",false). Therefore, we would expect them to be an instance of their own constructor. But, sadly, it is not the case...

Number.prototype instanceof Number //false
Number.prototype instanceof Number.prototype.constructor //false
 
//the best method so far to deal with it.
Object.prototype.toString.call(Number.prototype) //'[object Number]'

And many more...

why TypeOf-In help us:

TypeOf-In uses typeof-- instead of typeof and instanceof to retrieve the type. typeof-- extracts the constructor name or call Object.prototype.toString to get the type matching your value which allows this library to test all kinds of values accurately. Global Objects reference

TypeOf-In supports:

• Regex

• Multi choices

• primitive values and their respective wrapper return the same type

• NaN, undefined and null have their own types: #NaN, #Undefined and #Null

• it uses instanceof when necessary

• and more!

table of type returned by typeof-- (as string)

Usage:

    var typeOf = require('typeof-in'); 

Through an object

basic:

You can retrieve the type of your value as string by using getType

typeOf('lollipop').getType(); //'String'

Or you can test your value with a string representing an expected type, or by using its constructor. For performance issues, you would prefer to use strings as much as you can, and also because only a few constructors are supported by all browsers (example: Promise, IndexedDB API...).

//better performances, support multi-platform
typeOf('lollipop').In('String');             //'String' === 'String'
typeOf(new String('lollipop')).In('String'); //'String' === 'String'
typeOf(null).In('#Null');                    // '#Null' === '#Null'
 
//better readability, use instanceof when possible
typeOf('lollipop').In(String);             //'String' === 'String'
typeOf(new String('lollipop')).In(String); // x instanceof String
typeOf(null).In(null);                     // '#Null' === '#Null'

multi:

It is also possible to compare your value with a set of different types by using an array.

typeOf('lollipop').In([null, undefined, NaN, Number]); //false

regex:

Furthermore, TypeOf-In also supports RegEx against your value,

which is quite useful with < #####Error > or < HTML##### > types for example.

typeOf(new TypeError()).In(/.+Error$/); //all errors except 'Error'
typeOf(document.body).In(/^HTML.*/); //HTMLBodyElement [IE9+]

ES6 and others objects:

This library can check all kind of objects. Allowing you to compare ES6 features like Promises, Generators, fat arrows... which is pretty neat.

typeOf(new Promise(function(){})).In(Promise) 
typeOf(()=>{}).In(Function)
typeOf(function*(){}).In('GeneratorFunction')
//or, if we want to use instanceof
var GeneratorFunction = (function*(){}).constructor
typeOf(function*(){}).In(GeneratorFunction)

calling several times:

This is the main advantage of using TypeOf-In through an object, it allows you to deal with the same value in different ways

var myType = typeOf('test');
if(myType.In(String)){
    //do something with the value as a string
}else if(myType.In([null,undefined])){
    //you need to init your value!
}else if(myType.In(/.+Error$/)){
    //something bad happened! but not a global error
}else if(myType.In(Error)){ 
    //is type 'Error'... 
}

dealing with Objects:

This example shows different scenario where TypeOf-In will have a different behavior if the type is passed as a string or as a constructor.

Important: the library will not return an empty string("") but a "#Anonymous" type in the case of an instance of an anonymous constructor to improve readability.

    //use instanceof: return true
    typeOf({}).In(Object)
    typeOf({}).In({}) 
    typeOf([]).In(Object)
    typeOf([]).In(Array)    
    typeOf([]).In([])    
    typeOf(new TypeError()).In(Error)      
    typeOf(new TypeError()).In(TypeError)
    
    //use string comparison
    typeOf({}).In('Object') //true   
    typeOf([]).In('Object') //false
    typeOf([]).In('Array')  //true   
    typeOf(new TypeError()).In('TypeError')//true
    typeOf(new TypeError()).In('Error')    //false
        
    //more example ?
    
    function Human(){}; // ES6 equivalent: class Human {}
    var Person = Human;
    var Person2 = function Human(){};
 
    var person = new Person();
    var person1 = new Human();
    var person2 = new Person2();    
    
    typeOf(person).getType(); //'Human'
    typeOf(person2).getType(); //'Human'
    typeOf(person).In('Human'); //true
    typeOf(person2).In('Human'); //true
 
    //#instance against instance
    //if one of them has a valid constructor
    //use: x instanceof y.constructor; otherwise return false;
    typeOf(person).In(person1); //true 
    typeOf(person).In(person2); //false
        
    //#instance against constructor
    typeOf(person).In(Person); //true   
    typeOf(person).In(Human); //true   
    typeOf(person2).In(Human); //false    
    typeOf(person2).In(Object); //true
    
    
    //#special cases: instance of Anonymous (it behaves as the above examples)
    var AnonymousClass = function(){}, myAnonymous = new AnonymousClass();
    typeOf(myAnonymous).getType(); //return '#Anonymous'
    typeOf(myAnonymous).In('#Anonymous') //true
    typeOf(myAnonymous).In(AnonymousClass) //true    
    typeOf(myAnonymous).In(Object) //true   

Through a function

(decrease readability)

The recent version of typeof-in allows you to directly call the function in charge of the comparison, and by extension, not create an object every time you use typeOf() in your code.

This feature works exactly like the previous examples.

//for comparison: with one argument (default behavior)
typeOfIn('lollipop').In([Number, [], 'String']); 
 
//with more than one argument:
var typeOfIn = typeOf;
typeOfIn('lollipop','String');
typeOfIn('lollipop',[Number, [], String]); 
 
//with zero argument : TypeOf-In expose getType() and In().
var typeOf = require('typeof-in')();
typeOf.getType('lollipop') //'String'
typoOf.In('lollipop',[Number, [], 'String']);

force Object.prototype.toString

It is possible to force the use of Object.prototype.toString in typeof-- by adding the string 'forceObjectToString' at the last parameter of the In and getType methods.

typeOf(new TypeError(),'forceObjectToString').getType();
typeOf(new TypeError(),'forceObjectToString').In('Error');
 
var typeOfIn = typeOf;
typeOfIn(new TypeError(),'Error','forceObjectToString');
 
var typeOf = typeOf();
typeOf.getType(new TypeError(),'forceObjectToString');
typeOf.In(new TypeError(),'Error','forceObjectToString')

with requireJS (AMD)

/*
make sure to change the paths and module names according to your projects.
*/
require.config({
            baseUrl: "/",
            paths: {
                'typeof--':'./typeof--', //typeof-- directory path
                'typeOf':'./index' //TypeOf-In: index.js file path
            }
        });
 
        requirejs(['typeOf'], function(typeOf) {
                console.log(typeof typeOf);
                console.log(typeOf(42).getType());
                console.log(typeOf(42).In('Number'));
        });

see the following example

TypeOf only

In the case you only need the function used to retrieve the type of your values as a string (like typeof), you might be interested by using typeof-- directly

NPM commands

npm install typeof-in --save

npm test

About the environment

This library was created with function.name in mind, therefore, you will have better performances with recent version of your favorites browsers and servers (Node.JS V4...).

Be careful with [IE6-8], some objects has different behaviors (like arguments or document object).

Sorry for the capital letter in the In() method. IE6 doesn't like when I use the in keyword in my code...

you should consider using lodash before TypeOf-In, especially for simple cases

Finally, I'm open to any suggestions