Unlimited arguments in a JavaScript function

Question

Can a JavaScript function take unlimited arguments? Something like this:

testArray(1, 2, 3, 4, 5...);

I am trying:

var arr = [];
function testArray(A) {
    arr.push(A);
}

But this doesn't work (output is only the first argument). Or the only way is:

function testArray(a, b, c, d, e...) {

}

Thanks

As an alternative, you could have one parameter - "unlimited" container such as array (or object) and then just pass everything as array, even if there is only `...([one_arg])`... — jave.web, May 31 '16 at 11:14
Note that to directly answer the question, [No you can't.](http://stackoverflow.com/questions/22747068/is-there-a-max-number-of-arguments-javascript-functions-can-accept) — Kaiido, May 17 '17 at 04:19

Pointy · Accepted Answer · 2014-11-29T23:53:59.287

71

There's a weird "magic" variable you can reference called "arguments":

function manyArgs() {
  for (var i = 0; i < arguments.length; ++i)
    alert(arguments[i]);
}

It's like an array, but it's not an array. In fact it's so weird that you really shouldn't use it much at all. A common practice is to get the values of it into a real array:

function foo() {
  var args = Array.prototype.slice.call(arguments, 0);
  // ...

In that example, "args" would be a normal array, without any of the weirdness. There are all sorts of nasty problems with "arguments", and in ECMAScript 5 its functionality will be curtailed.

edit — though using the .slice() function sure is convenient, it turns out that passing the arguments object out of a function causes headaches for optimization, so much so that functions that do it may not get optimized at all. The simple, straightforward way to turn arguments into an array is therefore

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

More about arguments and optimization.

edited Nov 29 '14 at 23:53

answered Jun 18 '11 at 12:40

Pointy

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There is nothing "magic" or weird about it, the arguments object is defined in ECMA-262. The only similarity it has with an array is that it's length property is one more than its highest numeric property name. Other than that, it's just an object with properties. – RobG Jun 18 '11 at 14:06
7

I was being poetic :-) And the "arguments" variable *is* weird - it's also got things like the "callee" property. – Pointy Jun 18 '11 at 14:06
@SmartLemon I'm not sure I know exactly what you mean. I was not trying to be unhelpful. Americans have no understanding of that expression beyond "extracting urine from it". – Pointy Mar 20 '13 at 03:03
1

Sorry xD. I guess its not the common expression around there. Its like making fun of it. In this case it is like you are making fun of the question as if we should know it anyway. – FabianCook Mar 20 '13 at 03:19
@SmartLemon ah I see :-) Well I wasn't really making fun of the question; the `arguments` object really is strange, and the designer of the language himself considers it to be a mistake now. – Pointy Mar 20 '13 at 14:49
2

Here in this its explained in detail http://stackoverflow.com/questions/5145032/whats-the-use-of-array-prototype-slice-callarray-0 – PHP Avenger May 14 '13 at 21:39

Lucien Greathouse · Answer 2 · 2016-05-17T08:41:15.123

33

As of ECMAScript 2015 (or ES6) we also have access to rest parameters that give us a slightly cleaner way to manage arguments:

function foo(a, b, ...others) {
    console.log("a and b are ", a, b);

    for (let val of others) {
        console.log(val);
    }
}

foo(1, 2, 3, 4, 5);

At the time of this writing, this is supported by Chrome 47+, Firefox 15+, and Edge. The feature is also available via both Babel and TypeScript transpiling down to ES5.

edited May 17 '16 at 08:41

answered Oct 21 '15 at 19:21

Lucien Greathouse

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Thank you, this is exactly what I was looking for. Especially the MDN link, I just couldnt remember the name of it. :) – Noitidart Mar 16 '16 at 04:43

score 9 · Answer 3 · answered May 17 '17 at 03:45

9

With ECMAScript 6, you can use rest of arguments syntax:

const testArray = (...args) => {
    console.log(args);
};

testArray(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

answered May 17 '17 at 03:45

Marius Tancredi

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AmerllicA · Answer 4 · 2021-12-31T09:21:33.500

3

There are some legacy methods but I prefer the ES6 and newer versions, So if I wanna implement this, I wrote it like below:

const func = (...arg) => console.log(arg);

Simple and cutting edge of tech.

edited Dec 31 '21 at 09:21

answered Oct 15 '18 at 10:51

AmerllicA

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This is not quite valid JavaScript. I recommend the other answers to this question for an explanation of this feature. – Lucien Greathouse Dec 31 '21 at 01:49
@LucienGreathouse, thanks for your comment, I added parenthesis, it works now, sorry for my bad. – AmerllicA Dec 31 '21 at 09:22

score 3 · Answer 5 · answered Sep 21 '19 at 01:58

3

Javascript ES5

function testArray(){
    for(index = 0; index < arguments.length; i++) {
        alert(arguments[index])
    }
}

Javascript ES6

const testArray = (...arg) => console.log(arg)

answered Sep 21 '19 at 01:58

Pengguna

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Nosaj Neirbo · Answer 6 · 2017-11-29T20:58:38.723

1

You can also just "cast" it, saving you the ugly loop:

var getArguments = function() {
    return arguments;
};

var foo = getArguments(1,2,3,4);

// console.log(foo.slice()); => TypeError: foo.slice is not a function

var foo = Object.values(foo); 

console.log(foo); // => [ 1, 2, 3, 4 ]

foo.push(5);

console.log(foo); // => [ 1, 2, 3, 4, 5 ]

edited Nov 29 '17 at 20:58

answered Nov 29 '17 at 20:41

Nosaj Neirbo

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2

score 1 · Answer 7 · edited Jul 27 '13 at 16:44

1

function toArray() {
   return arguments;
}

var myargs = toArray(1, 2, 3, 4, 5, 6);

The arguments keyword is available in every js function

edited Jul 27 '13 at 16:44

Timo Tijhof

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answered Jun 18 '11 at 12:41

Zoidberg

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`arguments` is not of "type" `Array`, its just a sort of "iterable", and that is pretty lame on JS side. – Cristian Garcia Jul 07 '14 at 18:52

score 1 · Answer 8 · answered Jun 18 '11 at 12:42

1

var arr = [];
function testArray() {
    Array.prototype.push.apply(arr, arguments);
}

answered Jun 18 '11 at 12:42

clyfish

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score 0 · Answer 9 · answered Sep 29 '20 at 06:52

const outputDiv=document.querySelector('.output');
const output=(...x)=>{
    return outputDiv.innerHTML=x;
}

output(1,2,3,4,['hello',5,6],true,null);

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Javascript Practice</title>
    <link href="https://fonts.googleapis.com/css2?family=Raleway:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;0,700;0,800;0,900;1,100;1,200;1,300;1,400;1,500;1,600;1,800;1,900&display=swap" rel="stylesheet">


    <style>
        body{font-family: 'Raleway', sans-serif; background-color: #060606;}
        .center{height:100vh; width: 100%; display: grid;align-items:center;justify-content: center;}
        .output{font-size: 15px;color: rgb(59, 59, 255);font-weight: 200;}
    </style>
    
</head>
<body>
    <div class="center">
        <div class='output'></div>
    </div>

    <script src="js.js"></script>
</body>
</html>

Please explain why/how this solves the problem, see [How To Answer](https://stackoverflow.com/help/how-to-answer) — jasie, Sep 29 '20 at 07:17

Unlimited arguments in a JavaScript function

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