create a prototype from a function javascript code example

Example 1: function prototype javascript

function Person(name) {
  this.name = name;
}
Person.prototype.getName = function() {
  return this.name;
}

var person = new Person("John Doe");
person.getName() //"John Doe"

Example 2: javascript prototype vs constructor function

function Class () {}
Class.prototype.calc = function (a, b) {
    return a + b;
}

// Create 2 instances:
var ins1 = new Class(),
    ins2 = new Class();

// Test the calc method:
console.log(ins1.calc(1,1), ins2.calc(1,1));
// -> 2, 2

// Change the prototype method
Class.prototype.calc = function () {
    var args = Array.prototype.slice.apply(arguments),
        res = 0, c;

    while (c = args.shift())
        res += c;

    return res; 
}

// Test the calc method:
console.log(ins1.calc(1,1,1), ins2.calc(1,1,1));
// -> 3, 3