In PHP there is func_num_args
and func_get_args
, is there something similar for JavaScript?
This question is related to
javascript
algorithm
function
arguments
marshalling
ES6 allows a construct where a function argument is specified with a "..." notation such as
function testArgs (...args) {
// Where you can test picking the first element
console.log(args[0]);
}
In ES6, use Array.from
:
function foo()
{
foo.bar = Array.from(arguments);
foo.baz = foo.bar.join();
}
foo(1,2,3,4,5,6,7);
foo.bar // Array [1, 2, 3, 4, 5, 6, 7]
foo.baz // "1,2,3,4,5,6,7"
For non-ES6 code, use JSON.stringify and JSON.parse:
function foo()
{
foo.bar = JSON.stringify(arguments);
foo.baz = JSON.parse(foo.bar);
}
/* Atomic Data */
foo(1,2,3,4,5,6,7);
foo.bar // "{"0":1,"1":2,"2":3,"3":4,"4":5,"5":6,"6":7}"
foo.baz // [object Object]
/* Structured Data */
foo({1:2},[3,4],/5,6/,Date())
foo.bar //"{"0":{"1":2},"1":[3,4],"2":{},"3":"Tue Dec 17 2013 16:25:44 GMT-0800 (Pacific Standard Time)"}"
foo.baz // [object Object]
If preservation is needed instead of stringification, use the internal structured cloning algorithm.
If DOM nodes are passed, use XMLSerializer as in an unrelated question.
with (new XMLSerializer()) {serializeToString(document.documentElement) }
If running as a bookmarklet, you may need to wrap the each structured data argument in an Error constructor for JSON.stringify
to work properly.
References
Similar answer to Gunnar, with more complete example: You can even transparently return the whole thing:
function dumpArguments(...args) {
for (var i = 0; i < args.length; i++)
console.log(args[i]);
return args;
}
dumpArguments("foo", "bar", true, 42, ["yes", "no"], { 'banana': true });
Output:
foo
bar
true
42
["yes","no"]
{"banana":true}
As many other pointed out, arguments
contains all the arguments passed to a function.
If you want to call another function with the same args, use apply
Example:
var is_debug = true;
var debug = function() {
if (is_debug) {
console.log.apply(console, arguments);
}
}
debug("message", "another argument")
The arguments is an array-like object (not an actual array). Example function...
function testArguments () // <-- notice no arguments specified
{
console.log(arguments); // outputs the arguments to the console
var htmlOutput = "";
for (var i=0; i < arguments.length; i++) {
htmlOutput += '<li>' + arguments[i] + '</li>';
}
document.write('<ul>' + htmlOutput + '</ul>');
}
Try it out...
testArguments("This", "is", "a", "test"); // outputs ["This","is","a","test"]
testArguments(1,2,3,4,5,6,7,8,9); // outputs [1,2,3,4,5,6,7,8,9]
The full details: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Functions_and_function_scope/arguments
The arguments
object is where the functions arguments are stored.
The arguments object acts and looks like an array, it basically is, it just doesn't have the methods that arrays do, for example:
Array.forEach(callback[, thisArg]);
Array.map(callback[, thisArg])
Array.filter(callback[, thisArg]);
Array.indexOf(searchElement[, fromIndex])
I think the best way to convert a arguments
object to a real Array is like so:
argumentsArray = [].slice.apply(arguments);
That will make it an array;
reusable:
function ArgumentsToArray(args) {
return [].slice.apply(args);
}
(function() {
args = ArgumentsToArray(arguments);
args.forEach(function(value) {
console.log('value ===', value);
});
})('name', 1, {}, 'two', 3)
result:
>
value === name
>value === 1
>value === Object {}
>value === two
>value === 3
You can also convert it to an array if you prefer. If Array generics are available:
var args = Array.slice(arguments)
Otherwise:
var args = Array.prototype.slice.call(arguments);
from Mozilla MDN:
You should not slice on arguments because it prevents optimizations in JavaScript engines (V8 for example).
In ES6 you can do something like this:
function foo(...args) _x000D_
{_x000D_
let [a,b,...c] = args;_x000D_
_x000D_
console.log(a,b,c);_x000D_
}_x000D_
_x000D_
_x000D_
foo(1, null,"x",true, undefined);
_x000D_
Yes if you have no idea that how many arguments are possible at the time of function declaration then you can declare the function with no parameters and can access all variables by arguments array which are passed at the time of function calling.
Source: Stackoverflow.com