Access argument name string inside the function

Question

Is it possible to access arguments name strings?!

function myFunction (a, b, c, d, e, f) {
    var obj = [];
    [].forEach.call(arguments, function(arg) {
        obj.push({
            // question is how to get variable name here?
            name: "a",// "a", "b", "c", "d", "e", "f"
            value: arg, //a, b, c, ,d, e, f
        })
    });
 return obj;
}

myFunction(1,2,3,4,5,6); // return [{name: "a", value: 1}, {name: "b", value: 2}...]

Note: I know using arguments is not a good practice. I want to know if this even possible or not?

How could myFunction return anything if it doesn't have a return statement? — David G
– David G, Commented Jun 25, 2012 at 17:28
I have yet to find a basic way to retrieve the names of the argument variables. Values is cake, names not so much. — j08691
– j08691, Commented Jun 25, 2012 at 17:36

Engineer · Accepted Answer · 2012-06-25 17:52:05Z

6

You could try something like this:

function myFunction (a, blabla, c, somethingElse, e, f) {
    var obj = [];
    //'(a, b, c, d, e, f)' 
    var tmp = arguments.callee.toString().match(/\(.*?\)/)[0];
    //["a", "b", "c", "d", "e", "f"] 
    var argumentNames = tmp.replace(/[()\s]/g,'').split(',');

    [].splice.call(arguments,0).forEach(function(arg,i) {
        obj.push({
            // question is how to get variable name here?
            name: argumentNames[i],
            value: arg
        })
    });
    return obj;
}

console.log(JSON.stringify(myFunction(1, 2, 3, 4, 5, 6)));
//Output-> [{"name":"a","value":1},{"name":"blabla","value":2},
//          {"name":"c","value":3},{"name":"somethingElse","value":4},
//          {"name":"e","value":5},{"name":"f","value":6}]

DEMO

answered Jun 25, 2012 at 17:52

Engineer

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11 Comments

Mohsen Over a year ago

Nice hack. callee is what I never thought about.

KooiInc Over a year ago

Yep, I agree. But consider reading developer.mozilla.org/en/JavaScript/Reference/… too

Engineer Over a year ago

@KooiInc Yes, callee is forbidden only in strict mode, but not in entire javascript at all.

user1106925 Over a year ago

+1 For finding a creative solution, though I'd agree that .callee shouldn't be used when you could use the function name.

KooiInc Over a year ago

@Engineer, it's not forbidden in non strict js, but it is deprecated for a number of reasons, very well explained here: stackoverflow.com/questions/103598/….

|

jackwanders · Accepted Answer · 2012-06-25 17:32:51Z

2

Are the function parameter names definied in the function definition, as you've written above? If so, you can just create an array in the function:

function myFunction(a,b,c,d,e,f) {
  var argNames = ['a','b','c','d','e','f'];
  ...
}

arguments will only ever contain a simple array of the arguments passed to the function. There is no default mapping from arguments to parameter names. That I'm aware of anyway

answered Jun 25, 2012 at 17:32

jackwanders

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1 Comment

jackwanders Over a year ago

Yes, but you don't have any choice in the matter. There's no practical way to access function parameter names. Maybe you can clarify the context in which you're attempting this; perhaps there is a better solution?

David G · Accepted Answer · 2012-06-25 17:58:58Z

0

This works:

function myFunction( _obj ) {

    var obj = [],
        names = [],
        args = arguments,
        len = function(o) {
            var a = [];

            for (var i in o) a.push(i);

            return a;
        };

    for (var i in _obj) names.push( i );

    [].forEach.call( len(_obj), function(a, b) {
        obj.push({
            name: names[b],
            value: args[0][names[b]]
        });
    });

    return obj;

}

console.log( myFunction({
    a: 1,
    b: 2,
    c: 3,
    d: 4,
    e: 5,
    f: 6
}));

Here is a DEMO

edited Jun 25, 2012 at 17:58

answered Jun 25, 2012 at 17:32

David G

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4 Comments

user1106925 Over a year ago

He wants the name, so the first argument would have name:"a", then name:"b", name:"c", etc. You're assigning "a" for every argument.

David G Over a year ago

@Mohsen I was able to change it. Instead of inputting the arguments individually, I made it able to take an object literal instead. This version does work.

Mohsen Over a year ago

Sorry, you have changed the question.

David G Over a year ago

What do you mean, this functions as you have intended?

KooiInc · Accepted Answer · 2012-06-28 06:20:16Z

0

For completeness: you can't use named parameters in javascript. If you want to use them (and thus be able to identify the parameter names), a workaround is to supply an object:

function myParams(params){
  var ret = [];
  for (var l in params){ 
   if (params.hasOwnProperty(l)){
    ret.push(l);
   }
  }
  return ret
}
myParams({a:1,b:2,c:3,d:null,e:null,f:null,g:11});
//=> [a,b,c,d,e,f,g]

See also...
And to be really complete: see this also

edited Jun 28, 2012 at 6:20

answered Jun 25, 2012 at 17:51

KooiInc

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Comments

cezarypiatek · Accepted Answer · 2014-02-03 17:41:03Z

0

You can invoke toString on the function and then use some kind of RegEx to parse result.



    function someFunction(a,b,c){}
    var functionString = someFunction.toString(); //return "function someFunction(a,b,c){}"
    var args = functionString.match(/^function (?:.*?)\((.*?)\)/);
    if(args[1])
    {
        var argsNames = args[1].split(",");
    }

I've tested it on FF and Chrome.

answered Feb 3, 2014 at 17:41

cezarypiatek

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Comments

KAUSHAL J. SATHWARA · Accepted Answer · 2015-07-29 06:21:59Z

0

Since item.product_image2 is a URL string, you need to put it in quotes when you call changeImage inside parameter.

My Function Onclick

items+='<img src='+item.product_image1+' id="saleDetailDivGetImg">';
items+="<img src="+item.product_image2+"  onclick='changeImage(\""+item.product_image2+"\");'>";

My Function

<script type="text/javascript">
function changeImage(img)
 {
    document.getElementById("saleDetailDivGetImg").src=img;
    alert(img);
}
</script>

answered Jul 29, 2015 at 6:21

KAUSHAL J. SATHWARA

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