How to get function name within dynamic object function in native javascript

Question

I am creating a js library that handle item operations from collection object directly as follow. I want to allow to add dynamic user defined object function for each item and make these function available through collection object directly with index (please see example implementation).

var item = function (obj) {
    this.foo = function () {
        alert("foo" + this.name);
    }
    for (var i in obj) {
        this[i] = obj[i]; //dynamic fields (overridable)
    }
}
var collection = function (list) {
    var self=this;
    this.items = [];
    if (list && list.length > 0) {
        for (var i in list) {
            var t = new item(list[i]); // create new item            
            for (var j in t) {
                if (typeof (t[j]) === "function") {
                    this[j]=function(index,arg1,arg2,arg3){                        
                        self.items[index][j](arg1,arg2,arg3); //not working (unreliable)
                        console.log(j) //undefined
                        // problem is here j cannot be visible from function handler.
                        //I need to call dynamic j function within handler
                    }
                }
                this.items.push(t); //push each item into collection
            }
        }
    }
}
var obj=new collection([
    {
        id:1,name:"apple",
        bar:function(arg){
            alert(arg+" "+this.name);
        }
    }
    ]);
    obj.foo(0); //equivalent to obj.items[0].foo();
    obj.bar(0,"parameter"); //equivalent to obj.items[0].bar("parameter");

As described in comments in above code snippet, I can't call item's function from collection function dynamically. How can I achieve this purpose. Please help me.

FUNCTION.name will get the function name, is that what you want? — Downgoat
– Downgoat, Commented Apr 27, 2015 at 4:43
Thanks, But function assigned to (dynamic) field is anonymous. what I want is to retrieve is field name. — user1147987
– user1147987, Commented Apr 27, 2015 at 4:59
I created a jsfiddle of your code, and it works without any changes. jsfiddle.net/avivshaked/o6g9k8s6 — Aviv Shaked
– Aviv Shaked, Commented Apr 27, 2015 at 5:05
@user1147987, I tried your code on fiddle and it works perfectly, I didn't get your problem can you have a look at "jsfiddle.net/w8npva2b"? — syms
– syms, Commented Apr 27, 2015 at 5:06
Yes it working for one item,but It's not working if there are more than one item in collection. — user1147987
– user1147987, Commented Apr 27, 2015 at 5:36

KyawLay · Accepted Answer · 2015-04-27 07:05:47Z

1

You cannot get related field name from scope of handler. What you need to do is to create new function object with field name, i.e. function name= field name. To do so, you have to do a little trick in specifying dynamic function of item to collection object. Within handler scope, you can cast function name via arguments.callee
Change this snippet

var t = new item(list[i]); // create new item            
        for (var j in t) {
            if (typeof (t[j]) === "function") {
                this[j]=function(index,arg1,arg2,arg3){                        
                    self.items[index][j](arg1,arg2,arg3); //not working (unreliable)
                    console.log(j) //undefined
                    // problem is here j cannot be visible from function handler.
                    //I need to call dynamic j function within handler
                }
            }
            this.items.push(t); //push each item into collection
        }

in to this:

this.items.push(new item(list[i]));    
        var t=this.items[this.items.length-1];
        for (var j in t) {
           if (typeof (t[j]) === "function") {
                this[j]=new Function( "return function " + j + "(idx,arg1,arg2,arg3){console.log(this.items[idx]);var fn = arguments.callee.toString().substr('function '.length);fn = fn.substr(0, fn.indexOf('(')); if(this.items[idx][fn])this.items[idx][fn](arg1,arg2,arg3);}")();                    
            }
          //  this.items.push(t); //push each item into collection
        }                    
                }

jsfiddle sample : http://jsfiddle.net/kyawlay/7528t7z8/1/

edited Apr 27, 2015 at 7:05

answered Apr 27, 2015 at 5:34

KyawLay

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2 Comments

user1147987 Over a year ago

Thanks alot. it's incredable. But when I add new item to collection it call first object what's the error as follow

var obj=new collection([     {         id:1,name:"apple",         bar:function(arg){             alert(arg+" "+this.name);         }     },{         id:2,name:"orange",         bar:function(arg){             alert("bar1 "+arg+" "+this.name);         }     }          ]);     obj.foo(1); //equivalent to obj.items[0].foo();     obj.bar(1,"parameter"); //equivalent to obj.items[0].bar("parameter");

KyawLay Over a year ago

It's because of your focus of assigning item to collection. I update answer please try that approach. jsfiddle sample : jsfiddle.net/kyawlay/7528t7z8/1

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