bind.js

function FunctionBind(this_arg) { // Length is 1.
  if (!IS_FUNCTION(this)) {
      throw new $TypeError('Bind must be called on a function');
  }
  // this_arg is not an argument that should be bound.
  var argc_bound = (%_ArgumentsLength() || 1) - 1;
  if (argc_bound > 0) {
    var bound_args = new $Array(argc_bound);
    for(var i = 0; i < argc_bound; i++) {
      bound_args[i] = %_Arguments(i+1);
    }
  }
  var fn = this;
  var result = function() {
    // Combine the args we got from the bind call with the args
    // given as argument to the invocation.
    var argc = %_ArgumentsLength();
    var args = new $Array(argc + argc_bound);
    // Add bound arguments.
    for (var i = 0; i < argc_bound; i++) {
      args[i] = bound_args[i];
    }
    // Add arguments from call.
    for (var i = 0; i < argc; i++) {
      args[argc_bound + i] = %_Arguments(i);
    }
    // If this is a construct call we use a special runtime method
    // to generate the actual object using the bound function.
    if (%_IsConstructCall()) {
      return %NewObjectFromBound(fn, args);
    }
    return fn.apply(this_arg, args);
  };

  // We already have caller and arguments properties on functions,
  // which are non-configurable. It therefore makes no sence to
  // try to redefine these as defined by the spec. The spec says
  // that bind should make these throw a TypeError if get or set
  // is called and make them non-enumerable and non-configurable.
  // To be consistent with our normal functions we leave this as it is.

  // Set the correct length.
  var length = (this.length - argc_bound) > 0 ? this.length - argc_bound : 0;
  %FunctionSetLength(result, length);

  return result;
}