twostep

TwoStep

A simple control-flow library for node.JS that makes parallel execution, serial execution, and error handling painless. Based on gist https://gist.github.com/1524578

In different to that gist was added test coverage, try ... catch blocks for all steps and some usefull wrappers.

Installation

npm install twostep

Usage

All callbacks are executing in theirs steps.

var TwoStep = require('twostep');
var FS = require('fs');

TwoStep(
  function one() {
    this.pass(__filename + ".bak");
    FS.readFile(__filename, 'utf8', this.slot());
  },
  function two(err, target, contents) {
    if (err) throw err;
    this.pass(target);
    FS.writeFile(target, contents, this.slot())
  },
  function three(err, target) {
    if (err) throw err;
    console.log("%s written to successfully", target);
    FS.readdir(__dirname, this.slot());
  },
  function four(err, fileNames) {
    if (err) throw err;
    this.pass(fileNames);
    var group = this.makeGroup();
    fileNames.forEach(function (filename) {
      FS.stat(filename, group.slot());
    });
  },
  function five(err, fileNames, stats) {
    if (err) throw err;
    this.pass(fileNames.filter(function (name, i) {
      return stats[i].isFile();
    }));
    var group = this.makeGroup();
    stats.forEach(function (stat, i) {
      if (stat.isFile()) FS.readFile(fileNames[i], 'utf8', group.slot());
    });
  },
  function six(err, fileNames, contents) {
    if (err) throw err;
    var merged = {};
    fileNames.forEach(function (name, i) {
      merged[name] = contents[i].substr(0, 80);
    });
    console.log(merged);
  }
);

This can be some simple if we will use wrappers.

var TwoStep = require('twostep');
var FS = require('fs');

TwoStep(
    TwoStep.simple(function() {
		this.pass(__filename + ".bak");
		FS.readFile(__filename, 'utf8', this.slot());
	}),
	TwoStep.throwIfError(function(err, target, contents) {
		this.pass(target);
		FS.writeFile(target, contents, this.slot())
	}),
	TwoStep.throwIfError(function(err, target) {
		console.log("%s written to successfully", target);
		FS.readdir(__dirname, this.slot());
	}),
	TwoStep.throwIfError(function(err, fileNames) {
		this.pass(fileNames);
		var group = this.makeGroup();
		fileNames.forEach(function(filename) {
			FS.stat(filename, group.slot());
		});
	}),
	TwoStep.throwIfError(function(err, fileNames, stats) {
		this.pass(fileNames.filter(function(name, i) {
			return stats[i].isFile();
		}));
		console.log(fileNames)
		var group = this.makeGroup();
		stats.forEach(function(stat, i) {
			if (stat.isFile()) {
				FS.readFile(fileNames[i], 'utf8', group.slot());
			}
		});
	}),
	TwoStep.throwIfError(function(err, fileNames, contents) {
		var merged = {};
		fileNames.forEach(function (name, i) {
			merged[name] = contents[i].substr(0, 80);
		});
		console.log(merged);
	}),
    TwoStep.simple(function(err) {
	    if (err) {
		    console.log('Do something to handle error');
	    }
    })
);

Wrapper TwoStep.throwIfError free you of all time writing

 if (err) throw err;
 

All steps throwIfError will be skipped. Error just will be passed through the steps. To handle it you can use

TwoStep.simple(function(err) {}) 

or something other function, that get error in first parameter. It's very usefull for common mechanism of error handling.

Test

In project folder just run:

npm install

After installtion run:

npm test