CLONE CLASS
Clone an ES6 Class as Another Class Name for Isolating Class Static Properties.
EXAMPLE
Run the following example by:
$ git clone [email protected]:zixia/clone-class.git
$ cd clone-class
$ npm install
$ npm run example
TypeScript
import * as assert from 'assert'
import {
cloneClass,
instanceToClass,
} from '../src/clone-class'
class Employee {
public static company: string
constructor(
public name: string,
) {
}
public info() {
console.log(`Employee ${this.name}, Company ${(this.constructor as any).company}`)
}
}
/**
* Example 1: `cloneClass()`
*/
const GoogleEmployee = cloneClass(Employee)
GoogleEmployee.company = 'Google'
const MicrosoftEmployee = cloneClass(Employee)
MicrosoftEmployee.company = 'Microsoft'
const employeeGg = new GoogleEmployee('Tom')
const employeeMs = new MicrosoftEmployee('Jerry')
employeeGg.info()
// Output: Employee Tom, Company Google
employeeMs.info()
// Output: Employee Jerry, Company Microsoft
/**
* Example 2: `instanceToClass()`
*/
const RestoreGoogleEmployee = instanceToClass(employeeGg, Employee)
assert(RestoreGoogleEmployee === GoogleEmployee, 'Should get back the Class which instanciated the instance)
assert(RestoreGoogleEmployee !== Employee, 'Should be different with the parent Class')
const anotherEmployee = new RestoreGoogleEmployee('Mary')
anotherEmployee.info()
// Output: Employee Mary, Company Google
The most tricky part of this code is (this.constructor as any).company
.
It will be very clear after we break down it as the following steps:
this.constructor
is the constructor function of the class, which shuold be the class function itself.company
is a static properity defined inEmployee
class, which will be set as a property on the class function.- So
this.constructor.company
is equal toEmployee.company
, except that we will not need to know the exact name of the class,Employee
in this case. We use this pattern is because we need to visit the class function even we do not know it's name.
API
We have two APIs for dealing with the classes:
cloneClass(OriginalClass)
: create a new Class that isextend
from theOriginalClass
which can isolate static properties for stored values, and return the new Class.instanceToClass(instance, BaseClass)
: get the Class which had instanciated theinstance
, which is theBaseClass
, or the child class ofBaseClass
, and return it.
cloneClass()
const AnotherClass = cloneClass(OrignalClass)
const instance = new AnotherClass()
instanceToClass()
const RestoredClass = instanceToClass(instance, OrignalClass)
assert(RestoredClass === AnotherClass, 'because `instance` was created by `new AnotherClass()`')
Constructor<T>
const NewableClass: typeof AbstractClass & Constructor<AbstractClass>
const instance = new NewableClass()
It seems useless at first, but if you want to use manage many Child Class for a Abstract Class with typings, then it will be a must have tool.
CHANGELOG
v0.6 (May 2018)
- add new function:
instanceToClass()
for getting back theClass
from an existinginstance
. - add new type:
Constructor<T>
for addingnew (): T
to abstract class declaration.
v0.4 (Apr 2018)
First publish version.
cloneClass()
work as expected.
v0.0.1 (Apr 23, 2018)
Initial version, code comes from Project Wechaty.
Learn more about the full story at Chatie blog: New Feature: Multi-Instance Support for Wechaty v0.16(WIP)
SEE ALSO
An UseCase of clone-class
can be found in an article writen by me from Chatie blog, it's also the place where this module comes from. It's Worth to spent some time to have a look if you are interested.
AUTHOR
COPYRIGHT & LICENSE
- Code & Docs © 2018 Huan LI <[email protected]>
- Code released under the Apache-2.0 License
- Docs released under Creative Commons