I often see function chaines like this:
db.find('where...')
.success(function(){...})
.error(function(error){...});
I'm working on validation library for my project and i wonder how can i do chaining like that. Greetings
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2 Answers
Just return the object you are operating on from your function calls.
function MyObject(x, y) {
var self = this;
self.x = x;
self.y = y;
return {
moveLeft: function (amt) {
self.x -= amt;
return self;
},
moveRight: function (amt) {
self.x += amt;
return self;
}
}
}
var o = MyObject(0, 0);
o.moveLeft(5).moveRight(3);
1 Comment
user949300
In a few cases you return a different object where it makes sense, e.g.
db.find() might return a ResultSet kind of thing, but, yes, in general, just return this.What you are referring is called Promise which is style of programming in Javascript to deal with asynchronous functions. More information here
http://blog.mediumequalsmessage.com/promise-deferred-objects-in-javascript-pt2-practical-use
In your specific scenario, you can use when for that. Here is some example code that can get you started
function validateUnique() {
var deferred = when.defer();
db.query(...query to check uniqueness here.., function(error, result){
// this is a normal callback-style function
if (error) {
deferred.reject(error);
} else {
deferred.resolve(result);
}
}
return deferred.promise(); // return a Deferred object so that others can consume
}
Usage
validateUnique().done(function(result){
// handle result here
}, function(error){
// handle error here
})
If you want to continue the chain
validateUnique().then(anotherValidateFunction)
.then(yetAnotherValidateFunction)
.done(function(result){}, function(error){})
P/s: The link for when https://github.com/cujojs/when
