easy-async
easy-async is a library that helps coordinate asynchronous tasks, similar to Promises and async.js.
Like Promises, you get a "control object" that wraps an asynchronous task. The control object allows you to declare what to do after (or at the same time) as the wrapped task.
Like async.js, easy-async will NOT attempt to plumb arguments through your tasks. Also like async.js, the tasks will fail fast if any task produces an error.
Examples
You can see the examples together in a script here
Tasks receive only one parameter, the callback provided by easy-async. Each task must call the callback, and easy-async will only look for one single argument and assume it's an error.
var exampleTask = function(callback){
console.log('starting task');
setTimeout(function(){
console.log('done with task');
callback();
}, 1000);
}
var exampleErrorTask = function(callback){
console.log('starting task');
setTimeout(function(){
callback(new Error('BOOM!'));
}, 1000);
};
To run through tasks in series, get the control object with 'start', then line up tasks with the 'thenStart' method on the control object:
easyAsync.start(exampleTask)
.thenStart(exampleTask)
.thenStart(exampleTask)
.thenStart(function() {
console.log('continuing after tasks in series');
});
To run tasks in parallel, use the 'andStart' method on the control object:
easyAsync.start(exampleTask)
.andStart(exampleTask)
.andStart(exampleTask)
.thenStart(function() {
console.log('continuing after tasks in parallel');
});
To attach an error handler, use the 'onError' method on the control object:
easyAsync.start(exampleTask)
.andStart(exampleTask)
.andStart(exampleErrorTask)
.thenStart(function() {
console.log('continuing after risky work');
})
.onError(function(err){
console.log('error handler received an error');
console.error(err);
});
API
The easy-fix module exports only one method: start
. The start
method returns the "control object" (kind of like a promise) which contains the other methods listed here.
start(callback, options)
Create and return the control object, and start the callback
task. The control object has the other methods listed here. The options
are the same as thenStart
and andStart
methods (listed below). As a convenience, the callback
can be null.
The callback
is called with exactly one argument (a callback) which it must call to continue the easy-fix asynchronous task execution.
thenStart(callback, options)
Run the callback
after all previous callbacks to thenStart
and andStart
have completed. Use this to declare tasks to run in series.
The callback
is called with exactly one argument (a callback) which it must call to continue the easy-fix asynchronous task execution.
andStart(callback, options)
Run the callback
in parallel with a previous callback from thenStart
, as well as any other other callbacks from successive calls to andStart
. Use this to declare tasks to execute in parallel.
The callback
is called with exactly one argument (a callback) which it must call to continue the easy-fix asynchronous task execution.
onError(callback)
Specify a custom error handler. The default error handler simply throws the error.
The error handler callback
is called with two arguments: (error, errorIndex)
.
The error
is the same error that was passed in to any task callback or caught by a try/catch block (when wrapWithTry
is specified as an option).
The errorIndex
is a count (starting at 1) of all errors encountered by this control object.
As an example use case, easy-async may be used to coordinate multiple tasks in parallel when preparing a response to a single web request. Several of the tasks may generate errors - and the errorIndex
may be used to guarantee that the error handler will only attempt to respond once to that web request.
changeDefaults(options)
Specify new default options, which apply to all futher tasks added with thenStart
and andStart
.
Options
Options can be specified per-task, or by calling the changeDefaults
method.
wrapWithTry
- If true, tasks will be wrapped in a try/catch block, and caught errors passed through theonError
handler. Default isfalse
.onError
- specify a custom error handler. The default error handler simply throws the error.
Stay up to date
As of June 2016, the new easy-async v1 has some very prudent breaking changes (and new features)! Please read the change log!