javascript - What is this line of Js code exactly doing? -

i learning objects in javascript , i'm using function construct object , adding method it. there's method change firstname of object, line this.changename=changename;
exactly do? if delete or alter changename function name else error occurs , nothing displayed. , deleting line of code leads error, seems it's essential code run can't figure out does.

<script>  function person(firstname, lastname, age){     this.firstname=firstname;     this.lastname=lastname;     this.age=age;     this.changename=changename;      function changename(name){         this.firstname=name;     } } me = new person("hazem", "khadash", 18); me.changename("bashar"); document.write(me.firstname); 

as understand code, me created, changeme() function called method person.lastname rendered on screen.

thanks.

function person(firstname, lastname, age) {     ...      function changename(name){         this.firstname=name;     } } 

creates function available inside function person. you've found, having makes me.changename(…) not work, because function isn't accessible outside person.

this.changename = changename 

makes function accessible outside person function can call me.changename later.

notice it's this.changename = changename, not this.changename = changename(). parentheses, call function , assign output this.changename; without parentheses, assigns reference function changename this.changename.

you change this, , equivalent:

function person(firstname, lastname, age) {     ...     this.changename = function(name){         this.firstname=name;     } } 

the best way write person "class" this:

function person(firstname, lastname, age) {     this.firstname = firstname;     this.lastname = lastname;     this.age = age; }  person.prototype.changename = function changename(name){     this.firstname = name; };