Delegates

An exported .NET delegate type is converted to a TypeScript function type definition:

[JSExport]
public delegate string ExampleCallback(int arg1, bool arg2);

export function ExampleCallback(arg1: number, arg2: boolean): string;

Then a JavaScript function can be passed to a .NET API that expects a delegate of that type, and the parameters and return value will be marshalled accordingly.

[JSExport]
public static class Example
{
    public static void RegisterCallback(ExampleCallback cb) { … }
}

Example.registerCallback((arg1, arg2) => 'ok');

This is one way for .NET to call back into JavaScript. Another way is to implement a .NET interface with a JavaScript class.