javascript apply on constructor, throwing “malformed formal parameter”

Question

thanks to wonderful responses to this question I understand how to call javascript functions with varargs.

now I\'m looking to use apply with a constructor

Answer 1

You can exploit the fact that you can chain constructors using apply(...) to achieve this, although this requires the creation of a proxy class. The construct() function below lets you do:

var f1 = construct(Foo, [2, 3]);
// which is more or less equivalent to
var f2 = new Foo(2, 3);

The construct() function:

function construct(klass, args) {

  function F() {
    return klass.apply(this, arguments[0]); 
  }; 

  F.prototype = klass.prototype; 

  return new F(args);

}

Some sample code that uses it:

function Foo(a, b) {
  this.a = a; this.b = b;
}

Foo.prototype.dump = function() {
  console.log("a = ", this.a);
  console.log("b = ", this.b);
};

var f = construct(Foo, [7, 9]);

f.dump();