Is it possible to add methods to JQuery's promise object?

Question

I want to add a catch method to JQuery\'s promise object so I don\'t have to type the following every time:

.then(null,function(dat         


        

Answer 1

You can create your custom then

$.Deferred().prototype.customthen = function(){
  $.Deferred().prototype.then.call(this, null, ,function(data){
    // handle error
    return $.Deferred().resolve().promise();
  })
}

You have added a new function named customthen to the prototype. So, this new function is available in all instances.

Now, you can use it as follows

.customthen();

Answer 2

Yes, it is possible, but I would strongly recommend not to do this. Rather use a proper promise library and assimilate your jQuery promises; so that you can use the libraries builtin (and correct) .catch() method - so that you can omit that return $.Deferred().resolve().promise(); line as well.

The problem with extending jQuery promises is that they don't inherit from a prototype which we could simply amend, but use a factory pattern (read the source). You'll need to decorate it:

jQuery.Deferred = (function($Deferred) {
    var Deferred = function(func) {
        var deferred = $Deferred(func),
            promise = deferred.promise();
        deferred.catch = promise.catch = function(fnFail) {
            return promise.then(null, fnFail);
        };
        return deferred;
    };
    return Deferred;
}(jQuery.Deferred));

Answer 3

Frankly, I wouldn't use jQuery "Promises" at all since they do not even follow the spec. Use the bluebird library, for example.