Implementing JS decorator for chaining Class methods

Question

How could I implement a decorator that makes all methods of a class automatically chainable?

I have the following class:

class MyClass {
  async foo() { console.log(1); }
  async bar() { console.log(2); }
}

I want to be able to do the following:

@chainableMethods
class MyClass {
  ...
}

const myInstance = MyClass();

myInstance
  .foo()
  .bar();

Berube

Answer 1

You could try this

function chainableMethods (constructor) {
  let funcs = Object.getOwnPropertyNames(constructor.prototype);
  for (var i in funcs) {
    let func = funcs[i];
    let oldFunc = constructor.prototype[func];
    constructor.prototype[func] = (...args) => {
      let result = oldFunc.apply(this, args);
      return result || constructor.prototype;
      // Using 'result ||' for cases when a function does return something useful
      // You can remove it if it doesn't suit your requirement. 
    }
  }
}

If you intend on running bar only after the promise of foo is resolved then I don't think that will be possible.

Nonstandard

I think you want result || this and you dont need the spread, just use arguments keyword. – Actinouranium

Using the spread in case there are multiple arguments. Initially I did not have the result || but added it in case there is a function which returns something useful. In such cases it's better to have an error in the system than blindly chain the events. – Nonstandard

This doesn't work. You cannot use an arrow function to create a (prototype) method, and you should not return the prototype object for chaining. – Emeraldemerge