Promise subclass with mechanism to report progress before resolving
npm install progress-promisePromise subclass with mechanism to report progress before resolving
executor resolve Promisereject Promiseprogress Executor function receives extra argument: progress, a function to be called to notify a listener before resolving.
``javascript
const ProgressPromise = require('progress-promise');
function longTask() {
return new ProgressPromise((resolve, reject, progress) => {
setTimeout(() => progress(25), 250);
setTimeout(() => progress(50), 500);
setTimeout(() => progress(75), 750);
setTimeout(resolve, 1000);
});
}
`
Invoked by progress function passed to executor
* Value from executorPromise rejects if progress handler throws.
javascript
longTask()
.progress(value => console.log(value + '%'))
.then(() => console.log('Done'));// 25%
// 50%
// 75%
// Done
`$3
* Array of Promise, or compatibleLike
Promise.all() but the results are passed to the progress listener as an Array after each completion.A custom property,
proportion is added to this results array containing the value of the number of Promises resolved divided by the total number of Promises.`javascript
function delay(duration) {
return new Promise(resolve =>
setTimeout(() => resolve(duration), duration));
}ProgressPromise.all([ delay(300), delay(100) ])
.progress(results => console.log('Progress', results))
.then(results => console.log('Resolved', results));
// Progress [ , 100, proportion: 0.5 ]
// Progress [ 300, 100, proportion: 1 ]
// Resolved [ 300, 100, proportion: 1 ]
`$3
* Input values to be passed to handler sequentially
* handler Invoked for each input value, must return Promise
* value From inputs arrayHandler is invoked once for each input value, starting with the first index and proceding after each Promise returned resolves.
Progress is reported the same as
ProgressPromise.all().`javascript
ProgressPromise.sequence([ 200, 100 ], value => delay(value))
.progress(results => console.log('Progress', results))
.then(results => console.log('Resolved', results));// Progress [ 200, proportion: 0.5 ]
// Progress [ 200, 100, proportion: 1 ]
// Resolved [ 200, 100, proportion: 1 ]
`Design Considerations
$3
The function that invokes each listener on progress updates only has a single argument available due to the lack of support for spread operators in the target Node.js version this package aims to support, 4.3.
javascript
value => this[LISTENERS].forEach(listener => listener(value))
`
If a normal (not arrow) function is used here, cannot be accessed before super() is called, making it impossible to bind to the listeners instance property.$3
The new ES6
Symbol()` type creates a non-enumerating value that can be used as a key on an object. Creating a key on an object instance with a Symbol can be similar to creating a private property if the Symbol is not shared. If Symbols are not available, a fallback string property key is used.MIT