Question

I’m trying to modify some existing JavaScript code which used apply() to pass an array to a member function normally expecting any number of parameters:

oldFoo: function( arg /* , ..., argN */ ) {
  ...
}

var ary = ...

oldFoo.apply($, ary)

... other stuff using ary ...

The new code still takes any number of parameters and I still have them as an array to pass in, but I also need to pass in a new parameter before the array

newFoo: function( someObject, arg /* , ..., argN */ ) {
  ...
}

var ary = ...

newFoo.apply($, ???, ary)

... other stuff using ary ...

So I know I can make a new version of ary with array methods which modify it in-place such as pop/push/shift/unshift but I want to do various things with my array so don’t want to modify it in place.

I know I can build a new temporary array by prepending someObject to it, but that seems to take several lines of code each time.

Is there a more expressive way to achieve what I want to do in about the same number of lines? Something I’m missing about apply or about array functions which return a new array rather than modifying one in-place? I’m already using jQuery so if it has something useful that vanilla JavaScript doesn’t have then that’s great too.

Answer 1

I would do:

newFoo.apply($, ['foo','bar'].concat(ary) );

That way you won’t modify any existing array of arguments. From MDN:

concat creates a new array consisting of the elements in the this
object on which it is called, followed in order by, for each argument,
the elements of that argument (if the argument is an array) or the
argument itself (if the argument is not an array).