seq.js

// Seq
// Author: Franck Marcia

module.exports = (function () {

    "use strict";

    function Seq() {
    	this._error = [];
    	this._cont = [];
    }

    Seq.prototype.step = function (step)  {
        if (step && (step.constructor === Function || step instanceof Seq)) {
            [].push.call(this, step);
        }
        return this;
    };

    Seq.prototype.error = function (step) {
        if (step && (step.constructor === Function || step instanceof Seq)) {
            this._error.push(step);
        }
        return this;
    };

    Seq.prototype.next = function () {
        var args = arguments.length ? arguments : void 0;
        if (this.length) {
            var step = [].shift.call(this);
            if (step.constructor === Function) {
                step.apply(this, args);
            } else {
                var self = this;
                step._cont.push(function () { self.next(); });
                step.next.apply(step, args);
            }
        } else if (this._cont.length) {
            this._cont.shift().apply(this, args);
        }
    };

    Seq.prototype.halt = function () {
        if (this._error.length) {
            var args = arguments.length ? arguments : void 0;
            this.length = 0;
            var error = this._error.shift();
            if (error.constructor === Function) {
                error.apply(this, args);
                if (this._cont.length) {
                    this._cont.shift().apply(this, args);
                }
            } else {
                error.next.apply(error, args);
            }
        }
    };

    return function () {
        return new Seq();
    };

}());

seq_test.js

seq = require('./seq');

var mySeq = seq();
mySeq
	// 1st step: use 1 arg; define a seq property; call next step without args
	.step(function (a) {
		console.log('TEST #1');
		var mySeq = this;
		setTimeout(function () {
			console.log(a);
			mySeq.value = 'step #2';
			mySeq.next();
		}, 100);
	})

	// 2nd step: use a seq property; call the next step with 2 args
	.step(function () {
		setTimeout(function () {
			console.log(mySeq.value);
			mySeq.next('step #3a', 'step #3b');
		}, 100);
	})

	// 3rd step: use 2 args
	.step(function (a, b) {
		setTimeout(function () {
			console.log([ a, b ].join(', '));
			mySeq.halt('halt #1', 'halt #2');
		}, 100);
	})

	// 4th step: never reached
	.step(function () {
		console.log('step #4: never reached');
		this.next();
	})

	// 5th step: never reached
	.step(function () {
		console.log('step #5: never reached');
	})

	// define handler to be called if the seq is halted
	.error(function (a, b) {
		console.log('halted with ' + a + ' and ' + b + ', ' + this.length + ' left');
	});

var seqSub1 = seq();
seqSub1
	.step(function () {
		setTimeout(function () {
			console.log('sub #1 - step #1');
			seqSub1.next();
			//seqSub1.halt();
			//seqMain.halt('-1-', '-2-');
		}, 100);
	})
	.step(function () {
		setTimeout(function () {
			console.log('sub #1 - step #2');
			seqSub1.next();
		}, 100);
	})
	.error(function() {
		console.log('sub #1 - halted');
	});

var seqSub2 = seq();
seqSub2
	.step(function () {
		setTimeout(function () {
			console.log('sub #2 - step #1');
			seqSub2.next();
		}, 100);
	})
	.step(function () {
		var seqSub2 = this;
		setTimeout(function () {
			console.log('sub #2 - step #2');
			seqSub2.next();
		}, 100);
	})
	.error(function() {
		console.log('sub #2 - halted');
	});

var seqError = seq()
	.step(function (a, b) {
		var seqError = this;
		setTimeout(function () {
			console.log('error - step #1 with (' + a + ', ' + b + ')');
			seqError.next();
		}, 100);
	})
	.step(function () {
		setTimeout(function () {
			console.log('error - step #2');
			seqError.next();
		}, 100);
	})
	.error(function() {
		console.log('error - halted');
	});

var seqMain = seq();
seqMain
	.step(mySeq)
	.step(function () { console.log('\nTEST #2'); this.next(); })
	.step(seqSub1)
	.step(seqSub2)
	.error(seqError)
//	.error(function () { console.log('main - halted') })
	.next('step #1');