In _.invoke source code, what is the args' role?

I just started to learn JS few months ago and I tried to understand what the "args" doing in "_.invoke" source code. Is there anyone who can answer this, please?

I read mdn .apply and read other _.invoke source codes, but couldn't understand.

  _.invoke = function (collection, functionOrKey, args) {
    if(typeof functionOrKey === "string") {
      return _.map(collection, function(item) {
        return item[functionOrKey].apply(item, args);
      });
    }
    else return _.map(collection, function(item) {
      return functionOrKey.apply(item, args);
    });
  };

test function is like this :

_.invoke(['dog', 'cat'], 'toUpperCase');
      });

      it('runs the specified method on each item in the array, and returns a list of results', function() {
        var upperCasedStrings = _.invoke(['dog', 'cat'], 'toUpperCase');

        expect(upperCasedStrings).to.eql(['DOG', 'CAT']);

in test function, there are no 'args', why!?

All that's happening is you're taking an argument or array of arguments to apply to the function being used to map over the collection - all three are arguments passed to the function.

It's similar to other methods you might find in libraries like Lodash/Underscore.js - it's essentially a custom mapping function, where you pass the arguments like so:

let mapped = _.invoke(arr, aFunc, ["anArgument", 2]);

If no arguments are passed, then the function passed doesn't need arguments - toUpperCase doesn't need arguments, so none are needed - therefore none are passed.