setters and getters in javascript - javascript

I am trying to learn classes and setters and getters in JavaScript .. but my code isn't working .. it alerts undefined .. here is my code
function Person () {
name:"something"
Person.prototype = {
get Name (){
return name;
},
set Name (val){
this.name = val;
}
};
};
var person = new Person();
alert(person.name);

This is the right way to set getters and setters in your example:
function Person () {
this.name = "something";
}
Person.prototype = {
get Name() {
return this.name;
},
set Name(val) {
this.name = val;
}
};
var person = new Person();
person.Name = 'example';
alert(person.name);

JS is based on prototypes, then u can define propertys:
function Person(){
this._name = '';
}
Object.defineProperty(Person.prototype, "name", {
get: function(){
return this._name;
},
set: function(value){
this._name= value;
},
enumerable:true,
configurable: true
});
Then u can set or get property "name"
var p = new Person()
p.name = 'Stackoverflow'
alert(p.name) // Stackoverflow
In ES6 u can use the keyword class, example:
class Person {
constructor() {
this.name = '';
}
}

Related

How to call the child constructor function method?

When I try to call the method( getdetails() method of Teacher ) of child constructor function the parent constructor method is being called . Isn't the child method supposed to shadow the parent method . How to call the child constructor method getDetails()?
let Person = function() { };
Person.prototype.personName = "Smith";
Person.prototype.age = 37;
Person.prototype.getDetails = function() {
return `Person Name: ${this.personName}. Age is ${this.age}`;
};
let Teacher = function() { };
Teacher.prototype.mainSubject = "Physics";
Teacher.prototype.getDetails = function() {
return `Main subject is ${this.mainSubject}`;
};
Teacher.prototype = Object.create(Person.prototype); // inheritance
let teacher1 = new Teacher();
console.log(teacher1.getDetails());
You assign a new object to Teacher.prototype therefore losing everything you assigned to it beforehand. You should create the object before everything else.
let Person = function() { };
Person.prototype.personName = "Smith";
Person.prototype.age = 37;
Person.prototype.getDetails = function() {
return `Person Name: ${this.personName}. Age is ${this.age}`;
};
let Teacher = function() { };
Teacher.prototype = Object.create(Person.prototype); // inheritance
Teacher.prototype.mainSubject = "Physics";
Teacher.prototype.getDetails = function() {
return `Main subject is ${this.mainSubject}`;
};
let teacher1 = new Teacher();
console.log(teacher1.getDetails());
But nowadays you could also use classes instead of functions.
class Person {
personName = "Smith";
age = 37;
getDetails() {
return `Person Name: ${this.personName}. Age is ${this.age}`;
}
}
class Teacher extends Person {
mainSubject = "Physics";
getDetails() {
return `Main subject is ${this.mainSubject}`;
}
}
let teacher1 = new Teacher();
console.log(teacher1.getDetails());

The equivalent to using __proto__?

I'm trying to use the revealing module pattern with inheritance. I seem to have it working fine, but it uses "__proto__", which I understand it's considered deprecated. Is there a better was to create the inheritance with out using "__proto__"?
var Person = (function() {
var _name;
var api = {
init: init,
getName: getName
}
return api;
function init(name) {
_name = name;
}
function getName() {
return _name;
}
}())
var Teacher = (function() {
var _subject = "Math";
var api = {
getSubject: getSubject,
say: say
}
api.__proto__ = Person;
return api;
function getSubject() {
return _subject;
}
function say() {
console.log("I am " + this.getName() + " and I teach " + _subject)
}
}());
Teacher.init("Bob");
Teacher.say() // I am Bob and I teach math
https://plnkr.co/edit/XbGx38oCyvRn79xnn2FR?p=preview
The direct equivalent – setting the prototype, still a bad idea – is Object.setPrototypeOf:
Object.setPrototypeOf(api, Person);
The normal way of creating an object based on a prototype with Object.create and then adding properties to it works fine here, though:
var api = Object.create(Person);
api.getSubject = getSubject;
api.say = say;
but ideally you would just use constructors:
class Person {
constructor(name) {
this._name = name;
}
getName() {
return this._name;
}
}
class Teacher extends Person {
constructor(name) {
super(name);
this._subject = 'Math';
}
getSubject() {
return this._subject;
}
say() {
console.log(`I am ${this.getName()} and I teach ${this.getSubject()}`);
}
}
var teacher = new Teacher('Bob');
teacher.say() // I am Bob and I teach math
without ES6:
function Person(name) {
this._name = name;
}
Person.prototype.getName = function () {
return this._name;
};
function Teacher(name) {
Person.call(this, name);
this._subject = 'Math';
}
Teacher.prototype = Object.create(Person.prototype);
Teacher.prototype.getSubject = function () {
return this._subject;
};
Teacher.prototype.say = function () {
console.log('I am ' + this.getName() + ' and I teach ' + this.getSubject());
};
var teacher = new Teacher('Bob');
teacher.say(); // I am Bob and I teach math

Write getters as a prototype

I'm working on making performance updates on my javascript code.
In Firefox I got this warning:
mutating the [[Prototype]] of an object will cause your code to run very slowly; instead create the object with the correct initial [[Prototype]] value using Object.create
I wrote some scripts to prove this, and the results are great: without mutation a simple script runs 66% faster.
But I have trouble converting my code without mutation, I can't write the getters:
This is what I have now:
// Class
function FooBar(options) {
this.options = options;
}
// Prototype
FooBar.prototype = {
// Getters
get a() {
return this.options.a;
},
get b() {
return this.options.b;
},
get ab() {
return this.options.a + this.options.b;
},
// Methods
displayOptions: function() {
console.log(this.options);
}
};
// Code
var options = {
a: 'foo',
b: 'bar'
};
var fooBar = new FooBar(options);
console.log(fooBar.a);
console.log(fooBar.b);
console.log(fooBar.ab);
fooBar.displayOptions();
The getters as a prototype using the this keyword in their return are the problem.
If I use Object.defineProperty the this keyword is wrong, unless I do it inside the constructor, but it would recreate the property on each instance of the class and slow my code down even further.
This works (I just messed up the syntax in my previous attempt):
// Class
function FooBar (options) {
this.options = options;
}
//Prototype getters
Object.defineProperty(FooBar.prototype, 'a', {
get: function() {
return this.options.a;
}
});
Object.defineProperty(FooBar.prototype, 'b', {
get: function() {
return this.options.b;
}
});
Object.defineProperty(FooBar.prototype, 'ab', {
get: function() {
return this.options.a + this.options.b;
}
});
// Methods
FooBar.prototype.displayOptions = function() {
console.log(this.options);
};
// Code
var options = {
a:'foo',
b:'bar'
};
var fooBar = new FooBar (options);
console.log(fooBar.a);
console.log(fooBar.b);
console.log(fooBar.ab);
fooBar.displayOptions();
For those who are curious about the benefits of converting scripts like this to run faster: Run following code and look to your output in the console (Chrome - 66% faster, Firefox - no difference (curious, since I got the warning from Firefox)):
// WITHOUT PROTOTYPING
var Person1 = function() {
this.name = 'myName';
this.changeName = function(name) {
this.name = name;
};
this.changeName2 = function(name) {
this.name = name;
};
this.changeName3 = function(name) {
this.name = name;
};
this.changeName4 = function(name) {
this.name = name;
};
}
// WITH PROTOTYPING, WITH MUTATION
var Person2 = function() {
this.name = 'myName';
}
Person2.prototype = {
changeName: function(name) {
this.name = name;
},
changeName2: function(name) {
this.name = name;
},
changeName3: function(name) {
this.name = name;
},
changeName4: function(name) {
this.name = name;
}
};
// WITH PROTOTYPING, WITHOUT MUTATION
var Person3 = function() {
this.name = 'myName';
}
Person3.prototype.changeName = function(name) {
this.name = name;
};
Person3.prototype.changeName2 = function(name) {
this.name = name;
};
Person3.prototype.changeName3 = function(name) {
this.name = name;
};
Person3.prototype.changeName4 = function(name) {
this.name = name;
};
// DO THE TEST
var i=0, len=1000000;
// TEST1
window.performance.mark('mark_test_start');
for(i=0;i<len;i++) {
p = new Person1();
p.changeName('myName2');
}
window.performance.mark('mark_test_end');
window.performance.measure('no-prototyping', 'mark_test_start', 'mark_test_end');
// TEST2
window.performance.mark('mark_test2_start');
for(i=0;i<len;i++) {
p = new Person2();
p.changeName('myName2');
}
window.performance.mark('mark_test2_end');
window.performance.measure('prototyping-with-mutation', 'mark_test2_start', 'mark_test2_end');
// TEST3
window.performance.mark('mark_test3_start');
for(i=0;i<len;i++) {
p = new Person2();
p.changeName('myName2');
}
window.performance.mark('mark_test3_end');
window.performance.measure('prototyping-without-mutation', 'mark_test3_start', 'mark_test3_end');
// OUTPUT tests
var items = window.performance.getEntriesByType('measure');
for (var i = 0; i < items.length; ++i) {
var req = items[i];
console.log(req.name + ': ' + req.duration.toFixed(2));
}

In OPP JS can you access a method declared inside a prototype function from the constructor?

I'm reading about OPP js and while going over an example and was wondering if in:
function Person(name){
this.name = name;
}
Person.prototype.sayName = function(){
var tempName = this.name;
var saySomething = function(){
console.log(tempName);
}
//return saySomething();
}
var person1 = new Person('chris');
is theres a way to fire the saySomething method from the constructor.
eg.
person1.sayName().saySomething() //which doesnt work obviously
Returning an object when sayName will work:
function Person(name) {
this.name = name;
}
Person.prototype.sayName = function() {
var tempName = this.name;
return {
saySomething: function() {
console.log(tempName);
}
};
};
var person1 = new Person('chris');
person1.sayName().saySomething(); // logs 'chris'

javascript private variable through inheritance

I'm stuck with a problem using javascript...
I want to declare a private variable in a class that can't be used from its sublclass...what I've tried is:
function Person(){
var _name
this.setName = function(name){
_name = name
}
this.getName = function(){
return _name
}
}
function GreetingPerson(){
var self = this;
self.sayHello = function(){
console.log(self.getName() + ': "Hello!"');
}
}
GreetingPerson.prototype = new Person()
GreetingPerson.prototype.contructor = GreetingPerson;
var manuel = new GreetingPerson()
manuel.setName('Manuel');
manuel.sayHello();
var world = new GreetingPerson()
world.setName('World');
world.sayHello();
manuel.sayHello();
console.log(manuel.name)
In this way the name variable is private, but it is also static, so the last wo sayHello method calls, will write the same output.
I've tried also changing the Person class in this way:
function Person(){
this.setName = function(name){
this.name = name
}
this.getName = function(){
return this.name
}
}
But in this way it is not longer private.
What is the correct way to achieve it?
EDIT: Using something like #teddybeard says, you can get it too:
function Person(){
var _name;
this.setName = function(name){
_name = name;
};
this.getName = function(){
return _name;
};
return this;
}
function GreetingPerson(){
Person.call(this);
this.sayHello = function(){
console.log(this.getName() + ': "Hello!"');
};
return this;
}
GreetingPerson.prototype = new Person();
GreetingPerson.prototype.constructor = GreetingPerson;
var manuel = new GreetingPerson();
manuel.setName('Manuel');
manuel.sayHello();
var world = new GreetingPerson();
world.setName('World');
world.sayHello();
manuel.sayHello();
console.log(manuel._name);
But I'm not pretty sure if this is actually ok. The problem is that if you don't do something like Person.call(this); inside the constructor of GreetingPerson, you will not create a new instance of Person and it will always use the same _name value.
Check out Eloquent Javascript if you have time. I think this code should work for your purposes of inheritance.
function Person() {
var _name
this.setName = function(name) {
_name = name
}
this.getName = function() {
return _name
}
}
function GreetingPerson() {
Person.call(this);
this.sayHello = function() {
console.log(this.getName() + ': "Hello!"');
}
}
// taken from Eloquent Javascript
function clone(object) {
function OneShotConstructor() {}
OneShotConstructor.prototype = object;
return new OneShotConstructor();
}
GreetingPerson.prototype = clone(Person.prototype);
GreetingPerson.prototype.contructor = GreetingPerson;
var manuel = new GreetingPerson()
manuel.setName('Manuel');
manuel.sayHello();
var world = new GreetingPerson()
world.setName('World');
world.sayHello();
manuel.sayHello();
console.log(manuel.name)​;​

Categories