debounce-async

A debounced function that delays invoking asynchronous functions.

Preliminaries

A debounced function groups sequential calls to a function within a period. Only the last call in the group is executed. The others are simply ignored with rejections as if no calls to them ever happened.

Say d is a debounced function of f, var d = debounce(f, 1000);, where f is an asynchronous function that returns a promise being resolved in 400ms since it gets called. Below is a depiction of a sequence of calls to d.

seconds elapsed    0         1         2         3         4
d called           - d d d d d - - - - - d d d d - - d - - - - -
                     x x x x |           x x x x     |
f called                     +-------> f             +-------> f
                                       |                       |
promise resolved                       +-> *                   +-> *

d denotes a call to function d, f denotes a call to function f, and * denotes a promise returned by f is resolved. x denotes a call to d returns a rejected promise.

Installation

npm install debounce-async --save

Usage

var debounce = require( 'debounce-async' );

/**
  * debounce(func, [wait=0], [options={}])
  *
  * @param {Function} func The function to debounce.
  * @param {number} [wait=0] The number of milliseconds to delay.
  * @param {Object} [options={}] The options object.
  * @param {boolean} [options.leading=false] Specify invoking on the leading edge of the timeout.
  * @param {cancelObj} [options.cancelObj='canceled'] Specify the error object to be rejected.
  * @returns {Function} Returns the new debounced function.
  */

This package aims at maintaining the same signature of the debounce function from lodash. Please report if there is discrenency.

Example

Promise

var debounce = require( 'debounce-async' );

var f = value => new Promise( resolve => setTimeout( () => resolve( value ), 50 ) );
var debounced = debounce( f, 100 );

var promises = [ 'foo', 'bar' ].map( debounced );
promises.forEach( promise => {
  promise
    .then( res => console.log( 'resolved:', res ) )
    .catch( err => console.log( 'rejected:', err ) )
});

// Output:
// rejected: canceled
// resolved: bar

In the example above, f is an asynchronous function which returns a promise. The promise is resolved with the input after 50ms. debounced is a debounced function of f with a delay of 100ms.

The debounced function is called twice consecutively by the callback of Array.proptotype.map, with 'foo' and 'bar' being the input value respectively. The two returned promises are next fullfilled by printing the resolved result or rejected error on the console.

This snippet results in the given output. The first promise was rejected while the second one was resolved. It is because the second call comes before the delay of 100ms since the first call fired.

async/await

Same thing when it comes to asynchronous ES7 async/await functions. Take the prior example and transform the f into an ES7 async function.

var f = async value => await new Promise( resolve => setTimeout( () => resolve( value ), 50 ) );

Same output can be expected.

Test

npm test

License

MIT. See LICENSE.md for details.

szchenghuang / debounce-async