Is there a way to add methods on the fly to a class using typescript?

Question

I am trying create some kind of mixin method that add methods to the prototype/class on the fly but I get errors such as

The property 'greetName' does not exist on value of type 'Greeter' any

and

The property 'greetName' does not exist on value of type 'Greeter' any

when I run the following code.

class Greeter {     greeting: string;     constructor (message: string) {         this.greeting = message;     }     greet() {         return "Hello, " + this.greeting;     } }  Greeter.prototype.greetName = function(name){         return this.greet() + ' ' + name; }  var greeter = new Greeter('Mr');  window.alert(greeter.greetName('Name')); 

It actually compiles to valid js and runs as expected. Is there a way to do this with out compiler warnings/errors?

Answer 1

This solution has the benefit of giving you type checking when you dynamically add a method:

class MyClass {     start() {      } } var example = new MyClass(); // example.stop(); not allowed   interface MyClass {   stop(): void; }  MyClass.prototype['stop'] = function () {     alert('Stop'); } var stage2 = example; stage2.stop(); 

Answer 2

There is another way to do this.

Greeter["SomeProperty"] = function() {      return "somevalue"; }; 

Works the same and uses the property indexer function in javascript and typescript doesn't complain.