I'm studying JavaScript and I saw this example from w3schools.com (yes, I know about w3fools):

```
<script>
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);
</script>

```

When I tried to remove the `this.changeName=changeName;` part, the function no longer functioned. My question is why is that part needed? There was no explanation about it, it was just there.