jeremykohn/typecheck.js

Check value/variable types and subtypes in JavaScript.

TypeCheck.js

TypeCheck is an improved version of JavaScript's typeof operator.

For example, typeof 12.0 simply returns 'number'. typeCheck.getType(12.0) provides more detailed information as well: ['number', 'finite', 'integer'].

And for an array, typeof [] in plain JavaScript just returns 'object'. JavaScript arrays are also objects, so typeCheck.getType([]) returns both: ['object', 'array'].

Here are the types, and subtypes of each type, that TypeCheck recognizes:

Type	Subtypes
'number'	'infinite', 'finite', 'integer'
'string'	'numericString', 'integerString'
'object'	'array', 'function', 'date', 'regexp'
'boolean'
'undefined'
'null'
'NaN'

These are mostly consistent with the types returned by the typeof operator.

However, unlike typeof in plain JavaScript:

• TypeCheck has separate types for null and NaN, whereas typeof considers null to be an 'object' and NaN (Not A Number) to be a 'number'.
• TypeCheck classifies 'function' as a subtype of 'object', whereas typeof considers it a 'function' only.
• TypeCheck also classifies 'regexp' as a subtype of 'object', whereas typeof in some older browsers considers a regexp to be a 'function' instead.

Usage

TypeCheck provides the following methods:

typeCheck.getTypes(valueToCheck);

getTypes returns an array of strings, which lists all of valueToCheck's types and subtypes.

typeCheck.typeMatch(valueToCheck, typeOrSubtype)

typeMatch returns true if the array returned by typeCheck.getTypes(valueToCheck) includes typeOrSubtype.