Typescript generics extending class and interface

Question

I have a Typescript class which includes a generic which needs to extend another class and implement an interface. Here is an example

interface IHasImage {
          


        

Answer 1

Typescript is not so restrictive as Java or C# so you can do things like that:

interface IHasImage {
    imageUrl():string; 
}

class Model {
}

// use the Model class like an interface
interface IHasImageModel extends IHasImage, Model{
}

class View<T extends IHasImageModel> {
    constructor(arg :T){
       arg.imageUrl();
    }
}

Edit: In TypeScript 1.6 you can use Intersection types:

interface IHasImage {
    imageUrl():string; 
}

class Model {
}

class View<T extends IHasImage & Model> {
    constructor(arg :T){
       arg.imageUrl();
    }
}

Answer 2

Missing in the example is what T will be:

In the example below i have added an implementation for T, that can be used as the generic constraint.

interface IHasImage {
  imageUrl():string; 
}

class Model {
}

class ModelWithImage extends Model implements IHasImage {

    imageUrl():string
    {
     return "http://thepetwiki.com/images/thumb/Kitten.jpg/400px-Kitten.jpg";
    }   
}


class View<T extends ModelWithImage>
{
    value:T;

    constructor(arg:T)
    {   
        this.value=arg;
    }       
}

Answer 3

It looks like this is the only way of doing it that I can find. Not perfectly clean but it does the right thing.

interface IHasImage extends Model{  
  imageUrl():string; 
}

class Model {
}

class View<T extends IHasImage> {
}

Here is a screenshot from the playground verifying that it works:

Edit: Added correct workaround.