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I'm trying to discover a pattern for combining multiple interfaces into one abstract class. Presently I can combine multiple interfaces via implements, but an interface cannot declare a constructor. When I must introduce a constructor I'm forced to use an abstract class. When I use a abstract class I must re-declare the entire composite interface! Surely I'm missing something?

interface ILayerInfo { a: string; } interface ILayerStatic { b(): string; } class Layer implements ILayerInfo, ILayerStatic { constructor(info: ILayerInfo); a: string; b(): string; }

ANSWER: Use new:

interface Layer extends ILayerInfo, ILayerStatic { new(info: ILayerInfo); } // usage: new Layer({ a: "" });
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Declaring a constructor on the same interface as the instance members doesn't really make much sense -- if you're going to pass in a type dynamically to use in a constructor, it's the static side of the class that would be restricted. What you would want to do is probably something like this:

interface Colorable { colorize(c: string): void; } interface Countable { count: number; } interface ColorCountable extends Colorable, Countable { } interface ColorCountableCreator { new(info: {color: string; count: number}): ColorCountable; } class ColorCounted implements ColorCountable { count: number; colorize(s: string) { } constructor(info: {color: string; count: number}) { // ... } } function makeThings(c: ColorCountableCreator) { var results: ColorCountable[]; for(var i = 0; i < 10; i++) { results.push(new c({color: 'blue', count: i})); } return results; } var items = makeThings(ColorCounted); console.log(items[0].count);

See also How does typescript interfaces with construct signatures work?

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It was the "new" keyword on the interface that I was missing! I didn't want the class at all. With "new" I can stick to interfaces.
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Here's a sample of a solution for inheriting multiple interfaces:

type ShowAllWithTypography = TypographyClampProps & ShowAllProps interface Props extends ShowAllWithTypography
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Yes, or you could do interface Props extends TypographicClampProps, ShowAllProps but that does not help with class inheritance, which does not allow for multiple base classes.
I think see what you're saying. This solution was for expecting props types in a react project, where I wanted to expect certain props in Child components, but extend the properties of my Props interface a bit further. This worked for me but your use case needs a constructor, yes?
I was using libraries written before typescript that used mixins as a way of implementing multiple inheritance. I needed to describe them, specifically the constructor. I used "new" in the interface to describe the constructor. I think your answer is addressing the question in a way I'm not understanding. It seems you're missing a "new" declaration.
Anything given the Props return type will have all the properties of ShowAllWithTypography. I could extend it further by using a {} after my last line. No ‘new’ keyword needed to assign a Type to an object. New keyword is good for calling a constructor, if my memory serves me accurately.

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