How can you do something with each argument in a JavaScript function?

Question

Given this function:

function foo( a,b,c ) {
    //
}

How can you do something, say use console.log() for each argument? I know you can see the arguments by using the arguments keyword. Arguments seems to return what looks like an Array (but is of type "object" [suprise.. not]) but it doesn't support .forEach, I am using Chrome.

I tried modifying the function to this, and expected it to work:

function foo( a,b,c ) {
    arguments.forEach(function( arg ){
        console.log( arg );
    });
}

You get the error that TypeError: Object # has no method 'forEach'.

Sampson · Accepted Answer · 2012-12-06 03:40:45Z

5

The arguments object doesn't have a forEach method, so you need to iterate over it either with a for loop, or a for...in loop.

function foo () {
    for (var i = 0; i < arguments.length; i++) {
        console.log(arguments[i]);    
    }
}

foo("Foo", { "bar": 0 }); // Output: Foo, Object {bar: 0}

Or

function foo () {
    for (var arg in arguments) {
        console.log(arguments[arg]); 
    }    
}

foo("Foo", "Bar"); // Output: Foo, Bar

edited Dec 6, 2012 at 3:40

answered Dec 5, 2012 at 21:36

Sampson

269k76 gold badges546 silver badges570 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

gen_Eric Over a year ago

Won't using for..in on arguments also iterate over the length, callee and other properties?

Sampson Over a year ago

@RocketHazmat No. The length property isn't enumerable. The descriptor for length in the example above is {value: 2, writable: true, enumerable: false, configurable: true}.

Caley Woods Over a year ago

In your second example why is arguments[arg] required? Why can't you just console.log(arg)? I see, I had a typo before, the arg keyword is an index.

Sampson Over a year ago

@CaleyWoods Because 'arg' represents a key, and not a value. So we have to pass that key once again to the arguments object in order to get the corresponding value.

Caley Woods Over a year ago

Jonathan Sampson - I've accepted your answer as I feel it answers the exact question I asked. It didn't address my next question (which is no fault of yours) but some of the other answers did illustrate using Array.protoype.forEach.call() which answered my next question of "How do you make arguments respond to forEach?". I believe your for...in solution is even more readable than calling .forEach.

|

beatgammit · Accepted Answer · 2012-12-05 21:38:55Z

3

Or you can use a hack:

Array.prototype.forEach.call(arguments, function (arg) {
    console.log(arg);
});

arguments isn't an array, but it's close enough that you can apply Array's prototype and use the regular array functions. We're just grabbing Array's implementation and applying it forcefully to arguments.

answered Dec 5, 2012 at 21:38

beatgammit

20.3k20 gold badges92 silver badges131 bronze badges

3 Comments

Caley Woods Over a year ago

This is again what I was headed towards. I commented an explanation on phant0ms answer.

beatgammit Over a year ago

You could further simplify this to Array.prototype.forEach.call(arguments, console.log, console) if you only want to log it, but I doubt that's what you're after.

Caley Woods Over a year ago

tjameson that is correct. I have another function I'm looking to call and just wanted a clean way to do that and avoid: someFn(a); someFn(b);

phant0m · Accepted Answer · 2012-12-05 21:37:36Z

2

From MDN:

// convert to array
var args = Array.prototype.slice.call(arguments);
args.forEach...

answered Dec 5, 2012 at 21:37

phant0m

17k6 gold badges52 silver badges84 bronze badges

2 Comments

Caley Woods Over a year ago

This is along the lines of what I was looking for. The answers about using a regular for loop were good answers but it let me to the question, "If arguments doesn't respond to forEach, how can I make it do that?". This answer answers the question I hadn't asked yet. With that said, is this something that needs to be done within each function or can I permanently convert the arguments object into an array (not saying I'd want to, just curious.) ?

phant0m Over a year ago

@CaleyWoods No, you can't do it permanently, you'll have to do it for each function.

meder omuraliev · Accepted Answer · 2012-12-05 21:36:13Z

1

Do a loop on arguments.length. arguments isnt an Array so it doesn't have the forEach prototypal method.

for ( var i = 0, l = arguments.length; i<l; ++i ) {
  doSomething( arguments[i] );
}

answered Dec 5, 2012 at 21:36

meder omuraliev

187k76 gold badges402 silver badges443 bronze badges

Comments

gen_Eric · Accepted Answer · 2012-12-05 21:36:42Z

1

Just use a normal for loop.

function foo( a,b,c ) {
    for(var i = 0, len = arguments.length; i < len; i++){
        console.log(arguments[i]);
    }
}

Or you can convert it to a real array.

function foo( a,b,c ) {
    var args = Array.prototype.slice.call(arguments);
    args.forEach(function( arg ){
        console.log( arg );
    });
}

answered Dec 5, 2012 at 21:36

gen_Eric

228k42 gold badges304 silver badges343 bronze badges

Comments

YardenST · Accepted Answer · 2012-12-05 21:37:05Z

0

var show_args = function (){

    for(var ar in arguments){
        console.log(arguments[ar])
    }
}

answered Dec 5, 2012 at 21:37

YardenST

5,2762 gold badges38 silver badges60 bronze badges

Comments

maerics · Accepted Answer · 2012-12-05 21:37:36Z

0

You can convert the "arguments" into an array by calling the array slice method on it:

function foo(a, b, c) {
  var argArray = Array.prototype.slice.call(arguments);
  argArray.forEach(function(x) {
    // ...
  });
}

answered Dec 5, 2012 at 21:37

maerics

158k47 gold badges277 silver badges299 bronze badges

3 Comments

phant0m Over a year ago

Submitted the the same solution the very same second... Impossible! This must be one of those strange quantum world things.

bzlm Over a year ago

@phant0m, low-hanging fruits exist in the normal world too. :)

phant0m Over a year ago

@bzlm I'm more surprised by the timing than the contents ;)

Collectives™ on Stack Overflow

How can you do something with each argument in a JavaScript function?

7 Answers 7

7 Comments

3 Comments

2 Comments

Comments

Comments

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

7 Comments

3 Comments

2 Comments

Comments

Comments

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related