Typescript class implementing interface with anonymous function

Question

I'm faced with a situation where I need to create a class using a third-party interface (more specifically D3).

I want to create a class implementing the D3.Force interface, but my compiler just wont have it.

class CustomForce<NodeDatum extends D3.SimulationNodeDatum> implements D3.Force<NodeDatum, any> {
    // Some more code at some point
}

This throws the following error:

Class 'CustomForce<NodeDatum>' incorrectly implements interface 'Force<NodeDatum, any>'. 
Type 'CustomForce<NodeDatum>' provides no match for the signature '(alpha: number): void'

By inspecting the definition for D3.Force, I see the following:

export interface Force<NodeDatum extends SimulationNodeDatum, LinkDatum extends SimulationLinkDatum<NodeDatum> | undefined> {
    (alpha: number): void;
    initialize?(nodes: NodeDatum[]): void;
}

How do I implement an anonymous function taking in alpha as argument?!

Nitzan Tomer · Accepted Answer · 2017-03-22 13:46:17Z

2

I don't think that you'll be able to create a class that implements this sort of interface.
The interface defines a function which also has a property named initialize which is a function, and as far as I know you can't do that using a class.

You can however do this:

function CustomForce<NodeDatum extends D3.SimulationNodeDatum>(): D3.Force<NodeDatum, any> {
    const force = function(alpha: number): void {
        ...
    }

    force.initialize = function(nodes: NodeDatum[]) {
        ...
    }

    return force;
}

answered Mar 22, 2017 at 13:46

Nitzan Tomer

166k51 gold badges330 silver badges307 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Øystein Amundsen Over a year ago

I suspected as such. Feels wrong to create a function in Typescript that has methods though...

Nitzan Tomer Over a year ago

Well, in js a function is an object, so technically there's no problem with that. I usually avoid that as well, but sometimes it's nice to have that option

Collectives™ on Stack Overflow

Typescript class implementing interface with anonymous function

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related