How to properly wrap constructors with decorators in TypeScript

Question

The process of wrapping a class with a decorator causes superclasses to be unable to access that classes\' properties. Why?

I have some code that:

1. Crea

Answer 1

If you like run code after and before constructor() with a decorator:

function ClassWrapper() {
    return function(target: any) {
        // save a reference to the original constructor
        var original = target;

        // the new constructor behaviour
        var f: any = function (...args) {
            console.log('ClassWrapper: before class constructor', original.name);
            let instance = original.apply(this, args)
            console.log('ClassWrapper: after class constructor', original.name);
            return instance;
        }

        // copy prototype so intanceof operator still works
        f.prototype = original.prototype;

        // return new constructor (will override original)
        return f;
    };
}
@ClassWrapper()
export class ClassExample {
    public constructor() {
        console.info('Running ClassExample constructor...');
    }
}

let example = new ClassExample();

/*
CONSOLE OUTPUT:
ClassWrapper: before class constructor ClassExample
Running ClassExample constructor...
ClassWrapper: after class constructor ClassExample
*/