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Mutually Exclusive JS Type Testring

The aim of this module is to completely partition the set of JS objects into a set of types T:

T = [Function, Object, Date, Number, String, Boolean, RegExp, Undefined, Arguments, Null, Array]

Prop. 1 For every JS object x, x has exactly one type in T where [typr] returns true for its typecheck.

Prop. 2 Whether or not an Object has keys and can be looped over is determined by t.hasKeys and is completely independent of the type found in prop 1.

Prop. 3 Number types can be partitioned into 3 sub-types:

  • isNaN
  • isInfinite
  • isNumeric i.e. !isNaN && !isInfinite

These properties are tested extensively.


Basic usage:

var typr = require('typr');
typr.isFunction(el); // true iff el is a function 

Read the very short API.

Object Keys

The reason for prop 2 is that Objects can masquerade othes instances like Functions, Strings, RegExps, Dates. Object.keys() (and for-in) will actually work on some of these. This does not mean they will have interesting keys, but they sometimes do!

A common trick in node modules to export a function, but additionally attach properties to it. Such an object will only be a Function by our partitioning (as that was its original construction), but it is Object-like.

If you would rather test for enumerability of properties, use the extra test for Object-likeness: hasKeys.

Note again that this may not be super intuitive:

var dualThing = new String("wee");
dualThing.prop = "hi";
Object.keys(dualThing); // [ '0', '1', '2', 'prop' ] 
t.isObject(dualThing); // false 
t.isString(dualThing); // true 
t.hasKeys(dualThing); // true 


$ npm install typr

Running tests

Install development dependencies

$ npm install

Run the tests

$ npm test


MIT-Licensed. See LICENSE file for details.