CODEWITHSUNDEEP
typescript
lavrton
lavrton

Reputation: 20308

How to define methods that create dynamically?

I have a class like:

class Shape {
   attrs : any = {};
   getWidth() : number {
       return this.attrs.x * 2;
   }
  /*some code*/
}

The class have a LOT of getters and setters methods like getProperty() and setProperty(). Almost all of them works in same way but with different properties. To avoid a lot of code duplication in class definition I add such methods dynamically:

function capitalize(str) {
    return str.charAt(0).toUpperCase() + str.slice(1);
}

function addGetter(constructor, attr, defaultValue) : void {
    var method = 'get' + capitalize(attr);
    constructor.prototype[method] = function() {
        var val = this.attrs[attr];
        return val === undefined ? defaultValue : val;
    };
}

// then add a lot of getters in fast way
addGetter(Shape, 'x');
// now we have shape.getX();
addGetter(Shape, 'y');
// now we have shape.getY();

It works really good for javascript. But what about typesctipt? I can not do the same thing as I will have an error:

var shape = new Shape();
shape.getX();    // Property 'getX' does not exist on type 'Shape'.

I know that I can create "fake" method in class definition then overwrite it. But looks ugly:

class Shape {
   attrs : any = {};

   getWidth() : number {
       return (this.attrs.x || 0) * 2;
   }
   // fake method
   getX() : number {
       return 0;
   }
  /*some code*/
}

// then overwrite
addGetter(Shape, 'x');

Do you now any good solutions for this use case?

Upvotes: 1

Views: 3510

Answers (1)

basarat
basarat

Reputation: 275927

function addGetter(constructor, attr, defaultValue) : void

This is effectively a mixin. There isn't a good story about mixins in TypeScript at the moment. There is documentation of how to type it : https://github.com/Microsoft/TypeScript/wiki/Mixins

You basically declare that these members exist but don't provide an implementation.

class Shape {
   attrs : any = {};

   getWidth() : number {
       return (this.attrs.x || 0) * 2;
   }
   // declared only
   getX: ()=> number;

  /*some code*/
}

// then define
addGetter(Shape, 'x');

Mixins are on the roadmap for 2.0 : http://github.com/Microsoft/TypeScript/wiki/Roadmap#20 Also you can start a discussion here : http://github.com/Microsoft/TypeScript/issues It would be great if you can come up with a proposal

Upvotes: 5

Related Questions