[JavaScript] prototype

function Person(name, first, second, third) {

this.name=name;

this.first=first;

this.second=second;

this.third=third;

}

Person.prototype.sum = function( ) {

return this.first+this.second+this.third;

}

var kim = new Person('kim', 10, 20, 30);

kim.sum = function(){

return 'this : '+(this.first+this.second+this.third);

}

var lee = new Person('lee', 10, 10, 10);

console.log("kim.sum()", kim.sum());

-> kim.sum() this : 60

console.log("lee.sum()", lee.sum());

-> lee.sum() 30