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Typecase

Typecase aims to provide a useful type of a given value. It is intended for standard dynamically typed JavaScript.

Types seem to be a commonly misunderstood subject in the world of JavaScript and can sometimes be difficult to manage even if you do understand it well. Typecase differentiates between different types from the perspective of the JavaScript language and common usage rather than other statically typed languages.

Why

• It's JavaScript (No extra compiling, no local software setup).
• Ideal for both lower and higher level development.
• Covers a range of commonly used types as well as dynamic types e.g. objectHTMLBodyElement.
• Type checking syntax for single return values (pure functions)
• Assign callbacks for various types - TBA
• Option to toggle between debug/prod mode (Similar to Object.freeze usage) - TBA
• Typecase serves as a type-checker but can be toggled as a function wrapper that simply returns a given value.

Install

npm install typecase;

import {type, typecase} from 'typecase';

---

.true

// Returns a Boolean of the expected value match.
type(value).true // true | false

.false

// Returns a Boolean of the expected value match.
type(value).false // true | false

.exist

// Value is neither null nor undefined.
type(value).exist // OR !type(value).exist

.empty

// Value is null, undefined or an emppty string ''.
type(value)empty // OR !type(value).empty

.zero

// Value is null, undefined or equal to 0.
type(value).zero // OR !type(value).zero

Types

typecase allows you to see types for what they are. When applicable, the object wrapper is shown by the prefix 'object'. Less common type classes (such as elements) will return undefined if the value is falsy. All other types return boolean values.

type (<value>).<type> // true | false

// Common types

// String
type('Hello World!').string
type(String()).string
type(new String()).objectString

// Number
type(1000).number
type(Number(1000)).number
type(new Number()).objectNumber

// Boolean
type(true).boolean
type(Boolean(true)).boolean
type(new Boolean()).objectBoolean

// Array
type([]).array
type(Array()).array
type(new Array()).array

// Function
type(()=>{}).function
type(function(){}).function
type(Function()).function
type(new Function()).function

// Date, Map, WeakMap, Symbol
type(new Date()).objectDate
type(Symbol('foo')).symbol
type(new Map()).objectMap
type(new WeakMap()).objectWeakMap

// RegExp
type(/Hello/).regExp
type(RegExp()).regExp
type(new RegExp()).regExp

// Null, undefined and NaN
type(undefined).undefined
type(null).null
type(NaN).NaN

// Objects 
type({}).object
type(<other objectObjects>).object

// Non-standard type examples
type(document.createElement('div')).objectHTMLDivElement    // true | undefined
type(document.body).objectHTMLBodyElement                   // true | undefined
...And so on.

.some()

Returns true if at least one of the types validate as expected. If not returns false. If the expected types are of an equivalent amount to the values supplied, each type and value will be compared in order. If not they will be compared sporadically.

type(value, value, value, value).some('string','objectDate', 'number', 'array')

type(value, value, value, value, value, value).some('string','objectDate')

.every()

Returns true if all types validate as expected. If not returns false. Values and expectedTypes must be of equal length.

type(value, value, value, value).every('string','objectDate','true','false')

.is

Reveals the type as a string.

type(10000).is // "number"

.class (TBA)

Reveals the raw object class.

type(null).class // "[object Null]"
type(NaN).class // "[object Number]"

typecase()

typecase serves as a type-checker but can be toggled as a function wrapper that simply returns a given value.

// Check a type
import {type, typecase} from 'typecase'

	const greeting = 'Hello World!';
if(type(greeting).string){
	console.log(greeting)
}

// Return the correct type or throw an error
const If = typecase({
				errorHandlers:{
					objectDate: function(value, type){throw new TypeError(`${value} is not of type ${type}`)}
				},
				silence: false, // Silence callbacks
				debug: true     // If false will parse all types without checks
			})

const someFunction = (value)=>{
	value = 2000  // Oh no
	return If(value).objectDate
}
const newDate = new Date()
someFunction(newDate) // Throws error

What this library is not

This library does not check if a value is an instance of another, use the instanceof operator:

someDOMElement instanceof Element // true

Alternatively (type check only)

 type(someDOMElement).is.includes('Element') // true

Typecase does not aim to tell you the specific "type" of sub-object it may contain, this is usually not important since you would likely need to check for existing properties, and if not then native properties will be sufficient.

For everything else kind-of type related, the native language will be sufficient.

Explanations.

• Although Array is an object 'array' is returned rather than 'objectArray' because it is not an intended object for Object use unlike i.e. new Boolean(). The same applies to RegExp.

• Although NaN is an invalid type-of 'number', because this is commonly problematic 'NaN' is returned instead.

• 'objectObject' is always returned as 'object' for simplicity.

• null is returned as "null" since typeof null // object is a mistake.

• 'empty' and 'zero' also check for non-existence.

• Typecase uses the most appropriate method for checking a type to be more inlline with compiler optimisations at runtime. Despite this consideration, it's alway best to use typeof where feasible.

MIT (c) 2018 Julien Etienne.