Adding support for calling function with `this` context (object/class methods)

[redux-saga]

Adding support for calling function with `this` context (object/class methods)

[murtraja]

using arrow functions instead of methods also does the trick
for example:
convert this code

export default class API {
  fetch() {
    console.log(this);
  }
}

to this

export default class API {
  fetch = () => {
    console.log(this);
  }
}

[voodoods]

In addition: Binding the class Object itself with yield call(MyClass.myMethod.bind(MyClass)) seems to preserve the this context as well, even though apply should be the solution of choice.

[pke]

Signatur of apply effect seems to have changed to apply(context, method...)

[yelouafi]

Seems a valid issue to me. yield call( backend.fetch.bind(backend) ) can not be tested easily, because the call backend.fetch.bind(backend) will return a different result each time it's called.

Adding context (this) support to the call effect is a bit awkward because the call(fn, ...args) is variadic (I dont feel also the form call(null, fn, ...args) for non-class functions)

I think we should provide another effect creator to handle this case like method(API, fetch, ...args)

[tappleby]

Would it make sense to keep it similar to Function.prototype.call and Function.prototype.apply?

call works as is, if you need binding use apply?

call(method, arg1, arg2, argN) // Could be an alias for apply(method, null, [arg1, arg2, argN])
apply(method, context, [arg1, arg2, argN])

[yelouafi]

@tappleby I agree. Your solution looks better

[yelouafi]

FYI. the new v0.4.0 supports the apply effect.

[inyono]

Nice, thanks 👍

[jgehrcke]

On the topic, from https://github.com/microsoft/TypeScript/wiki/'this'-in-TypeScript:

The biggest red flag you can keep in mind is the use of a class method without immediately invoking it. Any time you see a class method being referenced without being invoked as part of that same expression, this might be incorrect.

The same document lists the solution that @murtraja also mentioned: using an instance arrow function: https://github.com/microsoft/TypeScript/wiki/'this'-in-TypeScript#use-instance-functions

[jgehrcke]

I like what's documented today, this signature of the call() effect: call([context, fnName], ...args)

Same as call([context, fn], ...args) but supports passing a fn as string. Useful for invoking object's methods, i.e. yield call([localStorage, 'getItem'], 'redux-saga')