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GoWithTheFlow.js - async flow control with a zen touch - for node and browser

2011-07-17

GoWithTheFlow.js is a javascript asynchronous flow-control micro library which works in node.js and in browser. It allow to control how your asynchronous code is executed, sequentially or in parallel. Flow() is only 30lines.

How to use it

Let start with a basic example. 2 jobs run in sequence. The first job is a timeout so the result is delivered asynchronously, and a second job is run only after the completion of the first.

Flow().seq(function(next){
    console.log("step 1: started, it will last 1sec");
    setTimeout(function(){
        console.log("step 1: 1sec expired. Step 1 completed");
        next();
    }, 1000);
}).seq(function(next){
    console.log("step 2: run after step1 has been completed");
})

It will display the following

step 1: started, it will last 1sec
step 1: 1sec expired. Step 1 completed
step 2: run after step1 has been completed

Methods

In order to keep it as simple as possible, Flow has only 2 methods.

.seq(callback) to execute job sequentially

.seq() is used to execute functions sequentially. The callback parameter will be executed only after all previous jobs are completed. The callback signature is callback(next, error, result)

next(error, result) is the function to call when the job is completed. error is to notify an error to the next job. result to notify a result. error and result may be omitted, if so they are considered equal to undefined
error is the error send by previous jobs
result is the result send by previous jobs

for example

Flow().seq(function(next){
    console.log("first job");
    next(null, "result1");
}).seq(function(next, error, result){    
    console.log("second job. run *after* first job");
    next();
})

.par(callback) to execute job in parallel

.par() is used to execute functions in parallel. The callback parameter is the same as for .seq(). If multiple .par() are declared one after another, they are run in parallel. The first .seq() after them will receive all the error and result in Array. One array item per previous .par()

for example

Flow().par(function(next){
    console.log("job foo");
    next(null, "foo");
}).par(function(next){
    console.log("job bar");
    next(null, "bar");
}).seq(function(next, errors, results){
    console.log("job run *after* the completion of foo and bar");
    console.assert(errors.length == 2 && errors[0] === null && errors[1] == null)
    console.assert(results.length == 2 && results[0] === 'foo' && results[1] == 'bar')
    next();
})

That's it

Conclusion

GoWithTheFlow.js is available on github here under MIT license. If you hit bugs, fill issues on github. Feel free to fork, modify and have fun with it :)