pendings

Pendings

Better control of pending promises

Pendings provides better control of pending Promises by automatic managing resolve / reject callbacks.

Installation

npm install pendings --save

Example

In promise-based class sometimes we store resolve / reject callbacks for future promise fulfillment. E.g.:

class MyClass {
    waitSomeEvent() { 
        return new Promise((resolve, reject) => {
            this.resolve = resolve;
            this.reject = reject;
            this.request();
        });
    }
    
    onEvent(event) {
        this.resolve(event.data);
    }
    
    onError(event) {
        this.reject(event.data);
    }
}

Pendings library allows to simplify it:

const Pending = require('pendings').Pending;

class MyClass {
    constructor() {
        this.pending = new Pending();
    }    

    waitSomeEvent() { 
        return this.pending.call(() => this.request());
    }
    
    onEvent(event) {
        this.pending.resolve(event.data);
    }
    
    onError(event) {
        this.pending.reject(event.data);
    }
}

Moreover, it is useful for list of pending promises. The unique id is generated for each promise and allows to fulfill it:

const Pendings = require('pendings');

class MyClass {
    constructor() {
        this.pendings = new Pendings();
    }    

    sendDataAndWait(data) { 
        return this.pendings.add(id => {
            data.id = id;
            this.send(data);
        });
    }
    
    onEvent(event) {
        const data = event.data;
        this.pendings.resolve(data.id, data);
    }
    
    onError(event) {
        const data = event.data;        
        this.pendings.reject(data.id, data);
    }
}

API

• Pendings - controls list of promises
  • .add(fn) - calls fn and returns new promise. fn gets unique id as parameter
  • .set(id, fn) - calls fn and returns new promise with specified id
  • .has(id) - does promise with specified id exist
  • .resolve(id, value) - resolves pending promise by id with specified value
  • .reject(id, reason) - rejects pending promise by id with specified reason
  • .fulfill(id, reason) - rejects pending promise if reason is specified, otherwise resolves with empty value
• Pending - controls single promise
  • .call(fn) - calls fn and returns new promise
  • .resolve(value) - resolves pending promise
  • .reject(reason) - reject pending promise
  • .fulfill(reason) - rejects pending promise if reason is specified, otherwise resolves with empty value

License

MIT @ Vitaliy Potapov