Standard conventions for indicating a function argument is unused in JavaScript

javascript naming-conventions unused-variables
Andrew Grimm picture Andrew Grimm · Aug 25, 2015 · Viewed 30.6k times · Source

Are there any standard ways of marking a function argument as unused in JavaScript, analogous to starting a method argument with an underscore in Ruby?

Answer

T.J. Crowder picture T.J. Crowder · Aug 25, 2015

Just so we have an example to work from, this is fairly common with jQuery's $.each where you're writing code that doesn't need the index, just the value, in the iteration callback ($.each is backward relative to Array#forEach):

$.each(objectOrArrayLikeThing, function(_, value) { }
    // Use value here
});

Using _ is the closest I've seen to a standard way to do that, yes, but I've also seen lots of others — giving it a name reflective of its purpose anyway (index), calling it unused, etc.

If you need to ignore more than one parameter, you can't repeat the same identifier (it's disallowed in strict mode, which should be everyone's default and is the default in modules and class constructs), so you have do things like _0 and _1 or _ and __, etc.

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