Hello,
I have now used Node.js for some time and have encountered some typical
problems like the code flow. It's easy do design the code that flows
linearly, like make query to database or N times. Event the callbacks can
be handled easily with great libraries called async, q and hopefully the
yield and generators save us. But the problem a rises when you have
callbacks and there are branches which create you different execution then
linear, some business logic, error handling. So what would be best cases to
handle these situations ?
As a solution I provide example of event driven code flow, which is based
on the events and executing small function units. There are some problems
like namespacing the event names and how does the listeners affect the
overall performance.
Here is my example:
var util = require("util"),
events = require("events");
function MyStream() {
events.EventEmitter.call(this);
}
util.inherits(MyStream, events.EventEmitter);
MyStream.prototype.init = function() {
// Init all the listeners
this.on('user:create', this.create);
this.on('user:exists', this.userExists);
this.on('user:delete:done', this.createAccess);
this.on('user:access:tags', this.accessTags);
this.on('user:end', this.end);
// Shoot out first event
this.emit('user:create');
};
MyStream.prototype.create = function() {
console.log('We need to create user');
this.emit('user:exists');
};
MyStream.prototype.userExists = function() {
console.log('Delete the old user and try to create new');
this.emit('user:delete:done', { name: 'Jukka', age: 24 });
};
MyStream.prototype.createAccess = function(user) {
// Based on the user information create accesses
if (user.name === 'Jukka') {
this.emit('user:access:tags', [ 'books', 'computers', 'programming' ]);
} else {
this.emit('user:access:tags', [ 'normal-people' ]);
}
};
MyStream.prototype.accessTags = function(tags) {
// Write tags to database
console.log('Write tags to database');
this.emit('user:end');
};
MyStream.prototype.end = function() {
console.log('This is the last call');
};
// Application starts here
// Yes the error handling is missing
var stream = new MyStream();
stream.on("user:exists", function(data) {
console.log('Really the user exists we can all something else out');
})
stream.init();
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