JavaScript single argument or array

Question

I have a JavaScript function which currently accepts one argument:

foo(country) { ... } and so is used like foo('US')

I need to extend this function to accept one or multiple countries:

foo('US')
foo('US', 'CA', 'UK')
foo(['US', 'CA', 'UK'])

Is any syntax/keyword feature for this? In C# we have a params keyword for this

Jared Smith · Accepted Answer · 2020-10-02 16:00:06Z

5

Use a gather:

function(...args) {
   // do something with args
}

This is generally considered preferable to using arguments because arguments is a weird case: it isn't truly an array, hence the awkward old idiom you'll still sometimes see:

var args = Array.prototype.slice.call(arguments);

edited Oct 2, 2020 at 16:00

answered Oct 2, 2020 at 15:54

Jared Smith

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3 Comments

T.J. Crowder Over a year ago

It's called a "rest parameter," FWIW.

Jared Smith Over a year ago

@T.J.Crowder indeed, I just find "gather" and "spread" easier to explain to people, especially since the same operator does two opposite things depending on context.

T.J. Crowder Over a year ago

:-) Quite. (Psst, neither rest nor spread is an operator. ;-) )

Nina Scholz · Accepted Answer · 2020-10-02 15:59:10Z

3

You could take rest parameters ... and flat the array.

function foo(...args) {
    return args.flat();
}

console.log(foo('US'));
console.log(foo('US', 'CA', 'UK'));
console.log(foo(['US', 'CA', 'UK']));

answered Oct 2, 2020 at 15:59

Nina Scholz

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Comments

Raphael Serota · Accepted Answer · 2020-10-02 15:53:36Z

1

Yes. arguments.

foo(country){
    console.log(arguments)
}

It looks like an array. It's actually an object with numbered keys, but you can still loop through it and get the information you need.

answered Oct 2, 2020 at 15:53

Raphael Serota

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Comments

Derek Wang · Accepted Answer · 2020-10-02 15:54:10Z

1

arguments in function plays the same role as params in c#.

function foo() {
  console.log(arguments);
}

foo('a','b','c');
foo('a');

answered Oct 2, 2020 at 15:54

Derek Wang

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