JavaScript: Defining function inside function -

in w3schools example, not getting how changename works:

function person(firstname, lastname, age, eyecolor) {     this.firstname = firstname;     this.lastname = lastname;     this.age = age;     this.eyecolor = eyecolor;      this.changename = changename;      function changename(name) {         this.lastname = name;     } } mymother = new person("sally", "rally", 48, "green"); mymother.changename("doe"); document.write(mymother.lastname); 

http://jsfiddle.net/mrge4/

why have this.changename=changename, , function definition changename?

it defining method changename person objects - in sort of round-about way, equivalent (and better) way is:

this.changename = function(name) {   this.lastname = name; } 

(hence 'please not use w3school')