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Improved typeof detection for node.js and the browser.


Improved typeof detection for node and the browser.

Type Detect is a module which you can use to detect the type of a given object. It returns a string representation of the object's type, either using typeof or @@toStringTag. It also normalizes some object names for consistency among browsers.

The typeof operator will only specify primitive values; everthing else is "object" (including null, arrays, regexps, etc). Many developers use Object.prototype.toString() - which is a fine alternative and returns many more types (null returns [object Null], Arrays as [object Array], regexps as [object RegExp] etc).

Sadly, Object.prototype.toString is slow, and buggy. By slow - we mean it is slower than typeof. By buggy - we mean that some values (like Promises, the global object, iterators, dataviews, a bunch of HTML elements) all report different things in different browsers.

type-detect fixes all of the shortcomings with Object.prototype.toString. We have extra code to speed up checks of JS and DOM objects, as much as 20-30x faster for some values. type-detect also fixes any consistencies with these objects.

type-detect is available on npm. To install it, type:

$ npm install type-detect

You can also use it within the browser; install via npm and use the type-detect.js file found within the download. For example:

<script src="./node_modules/type-detect/type-detect.js"></script>

The primary export of type-detect is function that can serve as a replacement for typeof. The results of this function will be more specific than that of native typeof.

var type = require('type-detect');
assert(type([]) === 'Array');
assert(type(new Array()) === 'Array');
assert(type(/a-z/gi) === 'RegExp');
assert(type(new RegExp('a-z')) === 'RegExp');
assert(type(function () {}) === 'function');
(function () {
  assert(type(arguments) === 'Arguments');
assert(type(new Date) === 'Date');
assert(type(1) === 'number');
assert(type(1.234) === 'number');
assert(type(-1) === 'number');
assert(type(-1.234) === 'number');
assert(type(Infinity) === 'number');
assert(type(NaN) === 'number');
assert(type(new Number(1)) === 'Number'); // note - the object version has a capital N 
assert(type('hello world') === 'string');
assert(type(new String('hello')) === 'String'); // note - the object version has a capital S 
assert(type(null) === 'null');
assert(type(undefined) !== 'null');
assert(type(undefined) === 'undefined');
assert(type(null) !== 'undefined');
var Noop = function () {};
assert(type({}) === 'Object');
assert(type(Noop) !== 'Object');
assert(type(new Noop) === 'Object');
assert(type(new Object) === 'Object');

All new ECMAScript 2015 objects are also supported, such as Promises and Symbols:

assert(type(new Map() === 'Map');
assert(type(new WeakMap()) === 'WeakMap');
assert(type(new Set()) === 'Set');
assert(type(new WeakSet()) === 'WeakSet');
assert(type(Symbol()) === 'Symbol');
assert(type(new Promise(callback) === 'Promise');
assert(type(new Int8Array()) === 'Int8Array');
assert(type(new Uint8Array()) === 'Uint8Array');
assert(type(new UInt8ClampedArray()) === 'Uint8ClampedArray');
assert(type(new Int16Array()) === 'Int16Array');
assert(type(new Uint16Array()) === 'Uint16Array');
assert(type(new Int32Array()) === 'Int32Array');
assert(type(new UInt32Array()) === 'Uint32Array');
assert(type(new Float32Array()) === 'Float32Array');
assert(type(new Float64Array()) === 'Float64Array');
assert(type(new ArrayBuffer()) === 'ArrayBuffer');
assert(type(new DataView(arrayBuffer)) === 'DataView');

Also, if you use Symbol.toStringTag to change an Objects return value of the toString() Method, type() will return this value, e.g:

var myObject = {};
myObject[Symbol.toStringTag] = 'myCustomType';
assert(type(myObject) === 'myCustomType');