Angular - How to use arrow functions with arguments?

Question

I have a angular 4 app, and i'm trying to write a queue of actions. each action will be fired after the previous function finished and will get its parameters.

public activeRegistrationAndSync() {
    let actionsToPerformByOrder = [
       () => this.registrationComponent.activeFormValidators.apply(null, arguments),
       () => this.registrationComponent.register.apply(null, arguments),
       () => this.autoLogin.apply(null, arguments),
       () => this.postLogin.apply(null, arguments),
       () => this.checkout.apply(null, arguments)
    ];

    let defer = new Deferred<void>();
    let curPromise = defer.promise;

    //Build chain of acitons
    actionsToPerformByOrder.forEach(action => {
      curPromise = curPromise
        .then(action)
        .catch(err => this.error.emit(err));
    })

    //Active actions
    defer.resolve();
 }
 
 
 export class Deferred<T> {
  promise: Promise<T>;
  resolve: (value?: T | PromiseLike<T>) => void;
  reject:  (reason?: any) => void;

  constructor() {
    this.promise = new Promise<T>((resolve, reject) => {
      this.resolve = resolve;
      this.reject  = reject;
    });
  }
}

My problem is that arrow functions doesn't support arguments and using function() {} instead change the this reference.

arrow functions do support arguments: (arg1, arg2) => this.doSomethingWith(arg1, arg2) — JB Nizet
– JB Nizet, Commented Aug 15, 2017 at 8:23
If you really need to use function() { ... } instead, you can define let that = this; before, and use that in the functions instead. — Arg0n
– Arg0n, Commented Aug 15, 2017 at 8:23

Max Koretskyi · Accepted Answer · 2017-08-15 08:32:35Z

0

I suggest you use async/await to combine and run your actions. It's easy to read, here is the basic idea, modify it with your specific case:

async function activeRegistrationASync() {
  const actionsToPerformByOrder = [
    async (r) => {
      return Promise.resolve(3)
    },
    async (r) => {
      return Promise.resolve(r + 5)
    }
  ];

  let result;
  for (let action of actionsToPerformByOrder) {
    result = await action(result);
  }
  return result;
}

activeRegistrationASync().then((r) => {
  console.log(r);
});

answered Aug 15, 2017 at 8:32

Max Koretskyi

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4 Comments

Tal Humy Over a year ago

Can I chain the result of one function as the parameter of the next one without the need to know what each function should receive? I know it can be done using apply(null, arguments) but arguments doesn't work with arrow functions. I want to write a class that will build a queue of executable functions which each function result will be supplied as parameter to the next function.

Max Koretskyi Over a year ago

but that is exactly what I'm doing, I'm passing the result of one function to the next. without the need to know what each function should receive - what do you mean here?

Tal Humy Over a year ago

Yes . Thank you very much :-) I used what you wrote to build a actionsQueue class with addAction and execute functions

Max Koretskyi Over a year ago

@user3554268, great, consider accepting my answer then)

RidgeA · Accepted Answer · 2017-08-15 08:26:06Z

0

You can use spread operator like

(...rest) => console.log(rest)
You can use bind function

function func (/arguments/) {console.log(this. arguments)}

let a = func.bind(this)

answered Aug 15, 2017 at 8:26

RidgeA

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