an attempt to make the new operator dynamically invokeable

newOperator.js

// usage: newOperator(constructor, [arg1, arg2, ...])
// example: newOperator(Date, [1995, 11, 24])
//   => should be identical to new Date(1995, 11, 24)

function newOperator(constructor, args) {
  var i = args.length + 1
    , params = []
    , fn

  while (i--) params[i] = "$" + i

  params.push("return new $0(" + params.slice(1) + ")")

  fn = Function.apply(null, params)
  params = params.concat.apply(constructor, args)

  return fn.apply(null, params)
}

you changed function name, if it's d of course it's smaller ... I would still leave the (a||[]).length to make newOperator(Array) possible, as example

good point, fixed it.

a non-golfed version:

function newOperator(ctor, args) {
  var length, fn

  args || (args = [])
  length = args.length + 1
  fn = newOperator[length]

  fn || (fn = newOperator[length] = Function(
    "ctor", "args", "i",
    "return new ctor(" +
      Array(length).join(",args[i++]").slice(1) +
    ")"
  ))

  return fn(ctor, args, 0)
}

jed, no need to b=b||[] ... just b||[] because if length is zero Array(1).join("whatever") will be an empty string (join works with at least length 2 between 0 and 1) so the b, even if undefined, will be untouched ;-)

function d(
  a, // constructor function
  b, // arguments
  c  // placeholder for length
){
  return(                         // return the result of
    d[c=b?-~b.length:1] || (      // the cached function or
      d[c] = Function(            // a new function that takes
        "a,b,c",                  // a constructor, arguments, and an index
        "return new a(" +         // and returns a new instance of the constructor
          Array(c)                // with
            .join(",b[c++]")      // the inline arguments
            .slice(1) +           // (sliced to remove leading comma)
        ")"
      )
    )
  )(a,b,0)                        // called with the constructor and arguments
}

in that case, why define the array at all if args has no length? can we use this?

var length = args ? args.length + 1 : 0

[EDIT] so something like this:

function newOperator(ctor, args) {
  var length = args ? -~args.length : 0
    , fn = newOperator[length]

  fn || (fn = newOperator[length] = Function(
    "ctor", "args", "i",
    "return new ctor(" +
      Array(length).join(", args[i++]").slice(1) +
    ")"
  ))

  return fn(ctor, args, 0)
}

the minus tilde does not give us much more than +1, 2 readable chars with no necessary int cast.
I agree the creation of an empty Array per each call without arguments is way too redundant and also bigger than this solution:
d[c=b?b.length+1:1]
I have edited and as result 2 chars less and faster "no arguments" execution ;-)

doesn't leaving out the number cast mean that the length property could be used to inject code? i'm thinking where args is {length: "throw 'neener neener'"}.

well, the initial trick does not solve a thing here ... if you want to screw up functions that would work even with native arrays methods ...

uh .. wait, I know what you mean ... so yes, minus tilde then, updated :D