TypeTags

String Representations of Node.js Built-in Objects#

This package contains a list of default string representations of built-in objects and types of Node.js — see the full list here.

import { TypeTags } from 'typetags'

TypeTags.Array
// → [object Array]

TypeTags.Function
// → [object Function]

TypeTags.Float64Array
// → [object Float64Array]

TypeTags can be used with any object to get its class or retrieve its type tag.

TypeTags.get('Hey')
// → [object String]

It also has predicates to help us identify an object's type by its type tag.

TypeTags.isArray('yo')
// → false

View on GitHub

Installation#

NPM

npm install typetags

Yarn

yarn add typetags

API Reference#

The TypeTags object contains a set of properties, methods and predicates, each representing an object type. We can use it to check if an object's type tag matches the default tag of a data type.

import { TypeTags } from 'typetags'

const o = { foo: 'bar' }

if (o.toString() !== TypeTags.String) {
  doSomething()
}

Methods#

TypeTags can help us interact with Node.js built-in types and assign tags to our own objects.

Its .has method allows us to check if an object has a valid toString method.

import { TypeTags } from 'typetags'

const proto = {}

TypeTags.has(proto)
// → true

proto.toString()
// → [object Object]

We can also use both .get and .of to retrieve an object's type tag.

const { TypeTags } = require('typetags')

let o = { foo: 'bar' }

const before = TypeTags.of(o)
// → '[object Object]'

TypeTags.assign(o, 'Bazzinga')

const after = TypeTags.get(o)
// → '[object Bazzinga]'

Predicates#

TypeTags has a predicate for each of Node.js built-in types. There are three generic predicates to help us identify an object by its type group.

Predicate methods are named by adding is in front of a type's name.

declare type PredicateNames = `is${Types | NestedPredicates}`

To learn more about each predicate visit pages Types and Predicates or use the search menu.

Using TypeTags to detect Object Class#

Every object has a toString() method that is automatically called when the object is to be represented as a text value or when an object is referred to in a manner in which a string is expected.

By default, the toString() method is inherited by every object descended from Object. If this method is not overridden in a custom object, toString() returns "[object type]", where type is the object type. The following code illustrates this:

const o = new Object()
o.toString() // → [object Object]

Although using toString() in this way is unreliable, as objects can change the behavior of Object.prototype.toString() this library might be helpful when you need to compare objects' tags inside a procedure call or if you just need a quick reference.

const { TypeTags } = require('typetags')

function isArray(value) {
  return typeof value === 'object' && TypeTags.get(value) === TypeTags.Array
}

See Mozilla MDN Web Docs

Bundles#

esm

import { TypeTags } from 'typetags'

cjs

const { isDefaultTag } = require('typetags')

umd

<script src="dist/umd/typetags.min.js"></script>

Tests#

jest --coverage

------------------|---------|----------|---------|---------|-------------------
File              | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
------------------|---------|----------|---------|---------|-------------------
All files         |   96.02 |       65 |    83.7 |     100 |
 lib              |   98.21 |    53.85 |   57.69 |     100 |
  assign-tag.js   |     100 |      100 |     100 |     100 |
  constants.js    |     100 |      100 |     100 |     100 |
  get-tag.js      |     100 |      100 |     100 |     100 |
  initializers.js |     100 |       50 |       0 |     100 | 3-142
  utils.js        |    97.3 |      100 |   91.67 |     100 |
 lib/resources    |   95.17 |    85.71 |   93.94 |     100 |
  TType.js        |   90.79 |    81.82 |     100 |     100 | 73,98-105,129-146
  TTypeUtils.js   |     100 |    66.67 |      60 |     100 | 52,59,78-80
  TextUtils.js    |     100 |      100 |     100 |     100 |
  TypeTags.js     |     100 |      100 |     100 |     100 |
------------------|---------|----------|---------|---------|-------------------

Test Suites: 66 passed, 66 total
Tests:       2 skipped, 417 passed, 419 total
Snapshots:   0 total
Time:        5.342 s
Ran all test suites.
✨  Done in 6.72s.

TypeScript#

Using TypeScript? We've got you covered. Check out our d.ts declaration files. If you'd like to help us improve our type definitions, submit a new issue. Contributions are always welcome. ❤️