JSequencer

Motivation

imagin having large number of call backs in sequence, somthing like

getData(function(a){  
    getMoreData(a, function(b){
        getMoreData(b, function(c){ 
            getMoreData(c, function(d){ 
                getMoreData(d, function(e){ 
                    ...
                });
            });
        });
    });
});

how about running this as a sequence

var a = getData();
var b = getMoreData(a);
var c = getMoreData(b);
var d = getMoreData(c);
var e = getMoreData(d);

more readable, right ??

But for async operations, this is not practical, need some sort of sequencing , and this what JSequncer does

check below example

$(document).ready(function () {
    var result = 1;
    var sequencer = new JSequencer.Sequencer()
    .add(function () {
        return result * 100;
    })
    .add(function () {
        return result - 50;
    })
    .add(function (context) {
        context.pause();
        console.log('paused');
        $('#resume').click(function () {
            context.resume(result + 100);
        });
    })
    .add(function () {
        return result / 5;
    })
    .while(function () {
        return result < 50;
    })
    .do(function () {
        result = result + 1
    })
    .if(function () {
        return result > 50;
    })
    .then(function () {
        result = result + 1;
    })
    .elseif(function () {
        return result < 50;
    }, function () {
        result = result + 1;
    })
    .else(function () {
        result = result + 1;
    })
    .endif()
    .onStep(function (context) { console.log('on step executed'); })
    .onPaused(function (context) { console.log('on pause'); })
    .onResumed(function (context) { console.log('on resume'); })
    .onCompleted(function (context) {
        console.log('on finished');
        console.log(result);
    })
    .context();

    sequencer.start();
});

in previous code block

• create object of JSequencer
• use sequencer.add(callback) to register step in the sequence
• use sequencer.while(predicate).do(callback) to run step in a loop
• use sequencer.if(predicate).then(callback).else(callback).endif() to make conditional flow
• each callback function is passed context object as first parameter, and previous step result as second patameter

Features

• support for async operations

var result = 1;
var sequencer = new JSequencer.Sequencer()
.add(function () {
    return result * 100;
})
.add(function () {
    return result - 50;
})
.add(function (context) {
    context.pause();
    console.log('paused');
    $('#resume').click(function () {
        context.resume(result + 100);
    });
})
.onCompleted(function (context) {
    console.log('on finished');
    console.log(result);
})
.context();
 sequencer.start();

just with a call to context.pause() instructs the sequencer to pause, then in callback, just call context.resume('return value') to resume the sequence , passing your return value

---

• Ability to build logical sequence using

sequencer.if(predicate)
.then(thenBody)
.elseif(predicate, thenBody)
.elseif(predicate, thenBody)
.elseif(predicate, thenBody)
.elseif(predicate, thenBody)
...
...
.else(finalElseBody)
.endif() //end if block

---

• Ability to build while loops like

sequencer.while(predicate)
.do(whileBody)

---

• Also you can hook into execution flow, by methods like

onStep(callback); \\ called after a step is executed
onPaused(callback); \\ called after flow is paused
onResumed(callback); \\ called after flow is resumed
onError(callback); \\ called after a step fails in exception, enable to continue, or terminate
onFailed(callback); \\ called after flow failed to complete
onCompleted(callback); \\ called after flow completed successfully

---

• control over workflow using context parameter passed to every step

context.pause(); //pauses the flow on the current step
context.resume(data); // resume the flow, passing result of current step
context.break(); //complete the current step, backout from the flow
context.getResults();// returns array contains the result of each executed step in order
context.set('key', value);// set / updates a value to be read by subsquent steps
context.get('key');// get values stored in execution context by previous steps