Creating (my own) TypeScript Library

Question

Following the tutorial on this page I have the following JavaScript:

function A(id) {
    var about = {
        Version: "0.0.0.1",
    };

    if (id) {
        if (window === this) {
            return new A(id);//<-Error in typescript
        }

        this.e = document.getElementById(id);
        return this;
    } else {
        return about;
    }
};

A.prototype = {
    doSomething: function () {
        //Some logic
        return this;
    }
}

JavaScript Usage:

var result = A("test");//The type of result should be 'A'
result = new A("test");//The type of result should be 'A'
result = A("test").doSomething();//The type of result should be 'A'
result = new A("test").doSomething();//The type of result should be 'A'

I want to create a library based on TypeScript that has the same usage. How can that be done?

If I try to just put this in a '.ts' file and compile I get an error saying: Error TS2350: Only a void function can be called with the 'new' keyword.

Also I am not sure how the usage with and without the 'new' keyword can be achieved as I am trying to make a library in typescript that can be used in javascript and not to make the user have to use the 'new' keyword.

PS
I know I can create a javascript file with a '.d.ts' file but that is not the purpose.

Answer 1

TypeScript is trying to reconcile the multiple purposes of A() and doesn't have enough information to figure out what you want it to look like.

This works :

function A(id): void {
    if (window === this) {
        return new A(id);//<-Error in typescript
    }

    this.e = document.getElementById(id);
    return this;
};

let result = A("test");
result = new A("test").doSomething();

But adding the version return block is confusing the compiler because A is now acting like two totally different things.

If you want to force the compiler to ignore the complaint you can do this:

function A(id): void {
    var about = {
        Version: "0.0.0.1",
    };

    if (id) {
        if (window === this) {
            return new A(id);//<-Error in typescript
        }

        this.e = document.getElementById(id);
        return this;
    } else {
        return <any>about;
    }
};

let result = A("test");
result = new A("test").doSomething();

But I don't recommend it. What you are trying to do is part of what TypeScript is trying to protect against. I don't know of a way to make the typings on this one "just work".

---

Edit: In response to your comment, I recommend something more like this:

class A {
    public static about = {
        Version: "0.0.0.1"
    };

    private e: HTMLElement;

    constructor(id) {
        this.e = document.getElementById(id);
    }

    public doSomething() {
        //Some logic
        return this;
    }
}

let result = new A("test");
result.doSomething();

let about = A.about;

Answer 2

This is the final code I came up with thanks to MrHen help:

class A {
    public element;
    public test;
    public doSomething;

    constructor(id) {
        if (id) {
            if (window === this as any) {
                return new A(id);//<-Error in typescript
            }

            this.element = document.getElementById(id);
            this.test = function () {
                console.log("testing"); return this;
            };
            this.doSomething = function () {
                console.log("doing something"); return this;
            };

            return this;
        }
    }
}

let result = ((A as any)("test") as A).doSomething();
result = new A("test").doSomething();