I'm using require.js and one of my modules requires another one, but is not interested in its export (it's a jQuery plugin), i.e. in the code

define(['jquery', 'jquery.mousewheel', 'fabric'], function ($, something, fabric) {
  // ...
}

I'm not interested in something. Of course I can move the dependencies of which results I'm not interested in to the end of the array and just omit the corresponding "trailing" parameters to my function, but for readability I'd like to keep them as shown. Which leads me to the question...

What is the JavaScript idiom for marking ignored parameters in function definition?

Of course I know I can use any name which discourages me from using the variable:

someMethodWithCallback(1, 2, 3, function (dx, notinterested1, notinterested2, point) {
  // ...
});

and was quite surprised that the following works (in Chrome at least) (because undefined is not a keyword):

someMethodWithCallback(1, 2, 3, function (dx, undefined, undefined, point) {
  // ...
});

but of course changing undefined value inside the function is potentially very error-prone...

To ignore parameter value Perl has undef, StandardML has _; has JavaScript anything like that, at least on "folklore" level?

I'm using require.js and one of my modules requires another one, but is not interested in its export (it's a jQuery plugin), i.e. in the code

define(['jquery', 'jquery.mousewheel', 'fabric'], function ($, something, fabric) {
  // ...
}

I'm not interested in something. Of course I can move the dependencies of which results I'm not interested in to the end of the array and just omit the corresponding "trailing" parameters to my function, but for readability I'd like to keep them as shown. Which leads me to the question...

What is the JavaScript idiom for marking ignored parameters in function definition?

Of course I know I can use any name which discourages me from using the variable:

someMethodWithCallback(1, 2, 3, function (dx, notinterested1, notinterested2, point) {
  // ...
});

and was quite surprised that the following works (in Chrome at least) (because undefined is not a keyword):

someMethodWithCallback(1, 2, 3, function (dx, undefined, undefined, point) {
  // ...
});

but of course changing undefined value inside the function is potentially very error-prone...

To ignore parameter value Perl has undef, StandardML has _; has JavaScript anything like that, at least on "folklore" level?

• javascript
• undefined

• You can use the shim option to load jQuery plugins as well. stackoverflow./a/10813415/1331430 – Fabrício Matté Commented Sep 8, 2013 at 0:17
• I know, I do. However, I'm not interested in their export. – pwes Commented Sep 8, 2013 at 0:22
• shim: { 'jquery.mousewheel': ['jquery'] } won't create any export I believe. But back on to the main question, I'm not aware of any semantics for that. I'd just name the parameter properly and not use it. That at least makes it clear why the parameter is there in the first place. – Fabrício Matté Commented Sep 8, 2013 at 0:24
• Right, the shim won't create the export. But I have to put a 'placeholder' parameter for the export in the function anyway (which will be assigned undefined value). – pwes Commented Sep 8, 2013 at 0:30
• If you know the parameter will never be passed undefined or null, you can do this: someMethodWithCallback({}, {}, {}, function .... Mind you, modern JS engines will generate an empty pattern warning, which is why this is a ment rather than an answer. – Marcelo Cantos Commented Nov 7, 2017 at 20:30

1 Answer 1

The convention our team follows is the Erlang's one: prepend names of these variables with _. Actually, it's quite often used in jQuery callbacks:

$.each(someArray, function(_i, el) { ... });

This way you can still see the meaning of the ignored param, but at the same time understand that it's ignored indeed.