supporting static and non-static methods in interface typescript

Question

so apparently (i'm beginner) ts doesn't support static methods in the interface however there is a workaround explained it Val's answer. it works when your class has only static methods. but if my class is a combination of static and non-satic methods this will throw an error:

Class 'MyClass' incorrectly implements interface 'sampleInterface'.
  Property 'staticFunction' is missing in type 'MyClass' but required in type 'sampleInterface'

any idea how to support this?

export function staticDecorator<T>() {
    return (constructor: T) => {};
}

interface sampleInterface {
   staticFynction(/*something*/): promise<void>;
   nonStaticFynction(/*something*/): promise<void>;
}

@staticDecorator()
class MyClass implements sampleInterface  {
    public static staticFynction(/*something*/): promise<void>{
      //something
    }
    public nonStaticFynction(/*something*/): promise<void>{
      //something
    }
}

jcalz · Accepted Answer · 2019-03-08 02:18:13Z

7

Generally you need two interfaces; one for the instance side of the class, and one for the static side of the class. For example:

interface SampleInterfaceInstancePart {
  nonStaticFunction(/*something*/): Promise<void>;
}
interface SampleInterfaceStaticPart {
  staticFunction(/*something*/): Promise<void>;
}

Then you can use your staticDecorator to ensure that the class implements the static side, and the regular old implements clause to ensure that it implements the instance side:

@staticDecorator<SampleInterfaceStaticPart>()
class MyClass implements SampleInterfaceInstancePart {
  public static async staticFunction(/*something*/): Promise<void> { }
  public async nonStaticFunction(/*something*/): Promise<void> { }
}

Hope that helps; good luck!

answered Mar 8, 2019 at 2:18

jcalz

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1 Comment

jlang Over a year ago

Is it possible to ensure that the static interface is also implemented correctly by the class? So similiar to implements SampleInterfaceInstancePart but for the static part?

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