Function call from within nested object failing

Question

In the code below I want to make generic functions available through the constructor. The object is for handling calls to an API. But if I call this._isEmpty(obj) from events.POST it always returns false. Placing the body of the _isEmpty() function does give the desired result. How do I solve this? Any tips on improving this structure are welcome ofcourse. I looked up some similar questions on SO but the questions/answers I found do not have similar nesting.

I make the following call:

var assystBridge = new global.assystBridge();
response.setStatus(assystBridge.events.POST(request, response));

Object:

var assystBridge = Class.create();
assystBridge.prototype = {
    initialize: function() {
        // Generic functions go here
        function _isEmpty(obj){
            // Checks whether an object has properties
            // Used for checking whether any data was posted or not
            // Returns true or false
            return Object.keys(obj).length === 0;
        }
    },
    events: {
        POST: function(request, response){
            var data = request.body.data;
            var responseText = '';
            if(this._isEmpty(data)){
            //if(Object.keys(data).length === 0){   
                response.setBody({"response":"NO data was posted", "data": data});
                return 400;
            } else {
                return 201;
            }

        },
        GET: function(request, response){

        },
        DELETE: function(request, response){

        }
    },
    type: 'assystBridge'
};

How do you call events.POST? Do you instantiate the assystBridge class and then call instance.events.POST? I am asking in order to establish what the meaning of "this" is in events.POST when you call it. — Theodoros Klikas
– Theodoros Klikas, Commented Sep 20, 2016 at 15:42
I am surprised that you don't get an error when you call response.setStatus(assystBridge.events.POST(request, response)); if somehow assystBridge doesn't inherit an _isEmpty function from somewhere else, the code should have normally broken cause the way it is written _isEmpty is not a member of the class or the prototype, it is just private to the initialize method. — Theodoros Klikas
– Theodoros Klikas, Commented Sep 20, 2016 at 16:02
It is on a Java backend that uses Rhino to implement a JS interface. It has some quirks so you are quite right in your assesment — g_uint
– g_uint, Commented Sep 20, 2016 at 16:04

thanksd · Accepted Answer · 2016-09-20 15:52:23Z

1

If you move the generic function out of the initialize() method and have it be one of the properties of the prototype, then you can reference it via assystBridge.prototype._isEmpty().

For example:

assystBridge.prototype = {
    _isEmpty: function(obj) {
        // Checks whether an object has properties
        // Used for checking whether any data was posted or not
        // Returns true or false
        return Object.keys(obj).length === 0;
    },
    events: {
        POST: function(request, response){
            var data = request.body.data;
            var responseText = '';
            if(assystBridge.prototype._isEmpty(data)){
                response.setBody({"response":"NO data was posted", "data": data});
                return 400;
            } else {
                return 201;
            }

        },
    },
    type: 'assystBridge'
};

answered Sep 20, 2016 at 15:52

thanksd

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1 Comment

g_uint Over a year ago

So I made a top-level property genericFunctions which will hold all the generic functions, and added var gf = assystBridge.prototype.genericFunctions to events.POST. Now gf._isEmpty() works. Thanks!

Peter Seliger · Accepted Answer · 2016-09-20 16:25:43Z

Besides what already has been said and meanwhile got accepted too, you even might move a step further, creating a factory for assystBridge, thus being in much better control of handling function scope appropriately ...

var createAssystBridge = (function () { // - immediately invoked function expression
                                        //   acting as a generator for a factory that
                                        //   will be returned, thus creating a closure ...

    // ... due to shared code, that will be preserved within this closure.

    function isEmpty(obj) {
        // Checks whether an object has properties
        // Used for checking whether any data was posted or not
        // Returns true or false
        return Object.keys(obj).length === 0;
    }

    function postData(request, response) {
        var data = request.body.data;
        var responseText = '';
        if (isEmpty(data)){
            response.setBody({"response":"NO data was posted", "data": data});
            return 400;
        } else {
            return 201;
        }
    }
    function getData(request, response) {

    }
    function deleteData(request, response) {

    }

    function initializeAssystBridge() {

    }

    // returning the factory

    return function assystBridgeFactory() {
        var
            assystBridge = Class.create();
          //assystBridge = Object.create({});

        assystBridge.prototype = {              //  - assign shared code
            initialize: initializeAssystBridge, //    with every call
            events: {                           //    of this factory.
                POST    : postData,             //
                GET     : getData,              //
                DELETE  : deleteData            //
            },
            type: 'assystBridge'
        };
        return assystBridge;
    };

}());

var assystBridge = createAssystBridge();

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