Javascript: "Infinite" parameters for function?
Functions can access an array-like object called arguments
that contains all the arguments that they received
function print_my_arguments(/**/){
var args = arguments;
for(var i=0; i<args.length; i++){
console.log(args[i]);
}
};
And you can do the opposite conversion (call a function given a list of arguments) with the apply method:
// These are equivalent:
print_my_arguments(1,2,3);
print_my_arguments.apply(null, [1,2,3]);
// The first parameter to `apply` is the `this`.
// It is used when the function is a method.
foo.bar(1,2,3);
var f = foo.bar; f.apply(foo, [1,2,3]);
Some important points to note:
arguments
isn't an actual array and it has none of the usual array methods (slice, join, etc). You can convert it to an array with the following line:var args = Array.prototype.slice.call(arguments);
Slice is also useful if you want your array to only contain the non-named arguments that were received:
function foo(first_arg, second_arg /**/){ var variadic_args = Array.prototype.slice.call(arguments, 2); }
Not every browser can handle an arbitrarily large number of function parameters. Last time I tested this, in Chrome and IE there was a stackoverflow after some 200.000 arguments. If your function can receive an arbitrarily large number of arguments, consider packing all of those arguments in an regular array instead.
Those
/**/
comments that appear in the arguments lists for my examples are not mandatory. They are just a coding a convention that I use to mark my variadic functions and differentiate them from regular functions.// A quick glance would suggest that this function receives no // parameters but actually it is a variadic function that gets // its parameters via the `arguments` object. function foo(){ console.log(arguments.length); }
The modern way of doing this is using rest parameters:
function printArguments(...args) {
args.forEach((arg, index) => {
console.log(`Argument ${index}:`, arg);
});
}
printArguments('hello', true, new Date());
By using the ...args
syntax, all parameters are saved in an array named args
.
Except of Internet Explorer, all browsers already ship this feature in their newest version.
Fiddle: https://jsfiddle.net/Lbf0stst/