Question

function extend(o, p) {
    for(prop in p) {                        
        o[prop] = p[prop];                  
    }
    return o;
}
function o() {};
function p(){};
p.name='caicai';
p.show=function(){ alert(this.name);};
p.show(); // output p
extend(o, p);
o.show(); // output o

why the “output” in here? why not to output ‘caicai’.

function extend(o, p) {
    for(prop in p) {                        
        o[prop] = p[prop];                  
    }
    return o;
}
function o() {};
function p(){};
p.poo='caicai';
p.show=function(){ alert(this.poo);};
p.show(); // output 'caicai'
extend(o, p);
o.show(); // output 'caicai'

BUT in here ?
why the “output” in here? why not to output ‘caicai’.

Answer 1

First: This is not related to the extend function.

o and p are functions. Function.name ^[MDN] is a non-standard property and cannot be overridden.

Example:

> function foo() {}
  undefined
> foo.name
  "foo"
> foo.name = 'bar';  // assigning a new value
  "bar"
> foo.name           // does not work
  "foo"

If you’d declare o and p as objects, then it would work:

> var foo = {};
  undefined
> foo.name
  undefined
> foo.name = 'bar';
  "bar"
> foo.name
  "bar"