goog.inherits使用临时构造函数的优点是什么？

Question

From Google's Closure library:

goog.inherits = function(childCtor, parentCtor) {
  /** @constructor */
  function tempCtor() {};
  tempCtor.prototype = parentCtor.prototype;
  childCtor.superClass_ = parentCtor.prototype;
  childCtor.prototype = new tempCtor();
  /** @override */
  childCtor.prototype.constructor = childCtor;
};

What is the advantage to the temporary constructor that is created?

Is there a reason the code doesn't just look like this:

goog.inherits = function(childCtor, parentCtor) {
  /** @constructor */
  childCtor.superClass_ = parentCtor.prototype;
  childCtor.prototype = new parentCtor();
  /** @override */
  childCtor.prototype.constructor = childCtor;
};

Answer 1

The first snippet is not calling the parentCtor - it is not instantiating an object with invoking the constructor on it, it just inherits from the parentCtor.prototype - actually it's a workaround for Object.create (very old browsers lack support of it). See also Understanding Crockford's Object.create shim on how the tempCtor works and What is the reason [not] to use the 'new' keyword here? on the undesirability of calling the parent.

Answer 2

You can only use "new parentCtor" if: (a) it will succeed without any parameters (b) you want the values set on the "this" value in parentCtor on your prototype.

You see people do this in simple cases:

var C = function() {};
C.prototype = new P();

But you can see how this can fail if P is:

var P = function(a) {a.x()}  // throws if "a" is undefined.

The tempCtor avoids this.