0.0.1 • Public • Published


instof(<value>,<constructor>) => <boolean>
instof(<value>,<constructor_name>) => <boolean>

Tests to see if the prototype property of a constructor appears anywhere in the prototype chain of an value. This is an alternative to instanceof that actually allows to check any value not just objects, even primitives, undefined and null. Also the big advantage in comparance with instanceof is that using instof you can do check without explicit import of constructor to the module by specifying string name of it.


const instof = require('instof')

//=> true:

instof(undefined, 'Undefined')
instof(null, 'Null')

instof(global, 'Global')
instof(global, Object)

instof(window, 'Global')
instof(window, 'Window')
instof(window, 'EventTarget')
instof(window, 'Object')

instof(NaN, 'NotNumber')
instof(NaN, Number)
instof(NaN, 'Object')

instof(1/0, 'InfiniteNumber')
instof(-Infinity, 'InfiniteNumber')
instof(Infinity, Number)

instof(Object.create(null), 'Dictionary')
instof({}, Object)

instof(42, Number)
instof(42, 'Object')
instof('str', String)
instof('str', Object)

instof(async function () {}, 'AsyncFunction')
instof(async function () {}, Function)
instof(async function () {}, 'Object')

instof([], Array)
instof([], Object)

instof(new BigInt64Array(), 'BigInt64Array')
instof(new BigInt64Array(), 'TypedArray')
instof(new BigInt64Array(), Object)

//=> false:

instof(null, Object)

instof(Object.create(null), Object)

instof(BigInt(Number.MAX_SAFE_INTEGER), Number)

instof('str', Symbol)

instof({}, 'Dictionary')

instof(new Object(), 'Null')

instof([], 'TypedArray')

instof(new Int8Array(), Array)

Reserved constructor names

Reserved constructor names make possible to distinguish type of some special values from values with the real type. Historically, accessing the global object has required different syntax in different JavaScript environments. On the web you can use window, self, frames, in Node.js you must instead use global and constructor of this global value is 'Object'. Also there are not straightforward situations with null, NaN and Infinity values. To determine the constructor of such values the instof function uses the following constructor names:

  • 'Undefined' for undefined
  • 'Null' for null
  • 'Global' for global, window, etc.
  • 'NotNumber' for NaN
  • 'InfiniteNumber' for Infinity or -Infinity
  • 'Dictionary' for object without prototype that was created by Object.create(null)


Install on Node.JS with npm

npm install instof


MIT © Taras Panasyuk

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npm i instof

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