What is surrogate prototype swapping in javascript?

Question

In the underscore.js code, the comments state:

// Naked function reference for surrogate-prototype-swapping.
var Ctor = function(){};

• What is surrogate-prototype-swapping?

or

• Where can I find an article/clear documentation on surrogate-prototype-swapping?

Answer 1

Made possible by Blender's answer. Intended for those on my level.

Though it is not a real term the following is a breakdown of the intended meaning of surrogate-prototype-swapping by more complete commenting of the original underscore.js code.

// A function which will be used as a constructor function in order 
// to add a prototype to a new object. There is nothing special about
// this function, except how it will be used.
var Ctor = function(){};

// Create a shortcut to Object.create if it exists. Otherwise
// nativeCreate will be undefined
var nativeCreate = Object.create;

// An internal function that will use or act as a polyfill for
// Object.create, with some type checking built in.
var baseCreate = function(prototype) {
    // Check if the object passed to baseCreate is actually an object.
    // Otherwise simply return an object (from an object literal), 
    // because there is not a valid object to inherit from.
    if (!_.isObject(prototype)) return {};

    // If Object.create is implemented then return the value
    // returned by Object.create when the prototype parameter is
    // passed into it. If Object.create has already been
    // implemented there is no need to recreate it. Just return
    // its return value.
    if (nativeCreate) return nativeCreate(prototype);

    // If Object.create is not defined then Ctor comes into play.
    // The object passed to baseCreate is assigned to the prototype
    // of Ctor. This means when Ctor is called prototype will be
    // the prototype assigned to this (the keyword this).
    Ctor.prototype = prototype;
    // Because Ctor is called with the new keyword this (the
    // keyword this) is returned returned by Ctor. Thus, the
    // variable 'result' is assigned an object with a prototype
    // equal to baseCreate's parameter 'prototype'.
    var result = new Ctor;
    // Then to reset things Ctor.prototype is set to null.
    Ctor.prototype = null;
    // The newly created object, whose prototype is the object
    // passed to baseCreate is returned.
    return result;
};

Answer 2

"Surrogate prototype swapping" (which I doubt is a real thing to begin with) is using an object only to assign to its prototype. That variable is used only once:

// Naked function reference for surrogate-prototype-swapping.
var Ctor = function(){};

var nativeCreate = Object.create;

// An internal function for creating a new object that inherits from another.
var baseCreate = function(prototype) {
    if (!_.isObject(prototype)) return {};

    if (nativeCreate) return nativeCreate(prototype);

    Ctor.prototype = prototype;
    var result = new Ctor;
    Ctor.prototype = null;
    return result;
};

It is used to make a cross-browser version of Object.create. You can't create a new instance of a prototype object directly, so you create a temporary object with your prototype object as its prototype and return a new instance of that.