JavaScript: How does 'new' work internally

转自：http://stackoverflow.com/questions/6750880/javascript-how-does-new-work-internally

The 

new

 operator
uses the internal 

[[Construct]]

 method,
and it basically does the following:

Initializes a new native object

Sets the internal 

[[Prototype]]

 of
this object, pointing to the Function 

prototype

 property.

If the function's 

prototype

 property
is not an object (a primitive values, such as a Number, String, Boolean, Undefined or Null), 

Object.prototype

 is
used instead.

After creating the object, it calls the function, providing the object as its 

this

 value.

If the return value of the called function, is a primitive, the object created internally is returned.

Otherwise, if an object is returned, the object created internally is lost.

An equivalent implementation of what the 

new

 operator
does, can be expressed like this (assuming that the ECMAScript 5 

Object.create

 method
is available):