如何创建TypeScript类的实例？

Question

I have the following class:

export declare class FlashMessagesService {
    show: (text?: string, options?: Object) => void;
    grayOut: (value: boolean) => void;
}

And I try to create instance of class:

 import { FlashMessagesService } from 'angular2-flash-messages';
    let _flashMessagesService = new FlashMessagesService();

It invoke an error:

Cannot read property 'show' of undefined

I use this library

Answer 1

I don't think you problem is typescript per se, but with angular dependency injection and how components are composed instead.

If you look at the source code of the package you are using you will see that show function is actually implemented by the FlashMessagesComponent and not by FlashMessagesService itself .

So to create an instance of it on your own without angular's dependency injection it is going to be tricky because you would also need to provide an instance of the abstract class ChangeDetectorRef , which itself might depend on other stuff, so it might get really messy pretty quickly.

something like the code bellow might help you to start playing with it, but it is far from something you would want to use in the real world.

import { FlashMessagesService, FlashMessagesComponent } from 'angular2-flash-messages';
let _flashMessagesService = new FlashMessagesService();
let component = new FlashMessagesComponent(_flashMessagesService, { detectChanges: () => {}} );
console.log(_flashMessagesService.show) // [Function show]

---

EDIT:

I coded directly here on SO and could not test it (sorry :( ), now checking it more thoroughly it seems that FlashMessagesComponent it not exported , so I don't clearly see a way for you to create an instance without using FlashMessagesModule and angular dependency injection lifecycle.

Answer 2

You should create a constructor for your class before :

export class Flashmessages { 
    ...
    //other vars
    constructor(){
        this.myvar = "value";
    }
}