The syntax of the interface has me confused. It looks overloaded but when I try to create a function with either signature the compiler tells me that the other signature is missing. The goal is to mock the function for a Jest unit test.
interface SearchResultSetEachFunction {
promise(callback: (result: Result) => boolean): Promise<boolean>;
(callback: (result: Result) => boolean): void;
}
It's not overloaded, it a function that also has a property named promise. You can use Object.assign to create such an object:
let fn: SearchResultSetEachFunction = Object.assign(function (callback: (result: Result) => boolean): void {
}, {
promise(callback: (result: Result) => boolean): Promise<boolean> {
return Promise.resolve(false)
}
})
Or in newer versions of typescript you can use a function declaration and directly assign the promise member in the same scope as the declaration to have ts recogize it as a new memeber:
function mockSearchResultSetEachFunction(callback: (result: Result) => boolean): void {
}
mockSearchResultSetEachFunction.promise = function (callback: (result: Result) => boolean): Promise<boolean> {
return Promise.resolve(false)
}
let fn: SearchResultSetEachFunction = mockSearchResultSetEachFunction
