CODEWITHSUNDEEP
typescript
Lokomotywa
Lokomotywa

Reputation: 2844

Extending type definition in variable defined in lib.d.ts

I have legacy code to transform that makes use of mootools. Mootools introduces a new constructor function of 'Element' with two parameters. I did not find any type definition file for mootools, so I have to write my own.

The typescript standard library (lib.d.ts) defines Element as following: 

  var Element: { prototype: Element; new(): Element; };

which makes it impossible to extend an existing interface.

What I was obviously trying is 

interface Element {
        new(s: string, s2: any): Element;
}

But still, the compiler complains about 

var c = new Element('p',{});

as the contructor expected 0 arguments, but got 2. What is the preferred workaround here?

The mootools constructor function

var Element = this.Element = function(tag, props){
    var konstructor = Element.Constructors[tag];
    if (konstructor) return konstructor(props);
    if (typeof tag != 'string') return document.id(tag).set(props);

    if (!props) props = {};

    if (!(/^[\w-]+$/).test(tag)){
        var parsed = Slick.parse(tag).expressions[0][0];
        tag = (parsed.tag == '*') ? 'div' : parsed.tag;
        if (parsed.id && props.id == null) props.id = parsed.id;

        var attributes = parsed.attributes;
        if (attributes) for (var attr, i = 0, l = attributes.length; i < l; i++){
            attr = attributes[i];
            if (props[attr.key] != null) continue;

            if (attr.value != null && attr.operator == '=') props[attr.key] = attr.value;
            else if (!attr.value && !attr.operator) props[attr.key] = true;
        }

        if (parsed.classList && props['class'] == null) props['class'] = parsed.classList.join(' ');
    }

    return document.newElement(tag, props);
};



// Browser
  var Browser = this.Browser = parse(navigator.userAgent, navigator.platform);




if (Browser.Element){
    Element.prototype = Browser.Element.prototype;
    // IE8 and IE9 require the wrapping.
    Element.prototype._fireEvent = (function(fireEvent){
        return function(type, event){
            return fireEvent.call(this, type, event);
        };
    })(Element.prototype.fireEvent);
}

Upvotes: 3

Views: 905

Answers (1)

Kirill Dmitrenko
Kirill Dmitrenko

Reputation: 3619

You don't need to extend Element interface, what you need is to extend type of Element variable. That's a bit confusing, that's two separate entities from TS standpoint. Here's how you can do it:

declare const Element: { // If you do that in a .d.ts file, you don't need declare.
    prototype: Element; // Element here is interface, we leave it unchanged.
    new(): Element; // Standard constructor.
    new(s: string, n: number): Element; // Your custom constructor.
};

const e = new Element('1', 2);

e.nodeName; // => string, i.e. result object implements Element interface.

Upvotes: 1

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