Related
I have been learning JS on my own and completed an 8 hour course on the basics. Now I am following another course where the lecturer, as it seems to me, is creating a function using dot notation. I am not sure if this is what is happening and I am having a hard time understanding exactly what it is doing.
function Person(fName, lName) {
this.firstName = fName
this.lastName = lName
}
const person1 = new Person("Bruce", "Wayne")
const person2 = new Person("Bat", "Man")
person1.getFullName = function () {
return this.firstName + ' ' + this.lastName
}
console.log(person1.getFullName())
The part I am confused about is:
person1.getFullName = function () {
return this.firstName + ' ' + this.lastName
}
I see in the Person() function we are creating an object called person1 using "this" and a key to pass in parameters as values for those keys. However it looks to me like there is a function being assigned to the person1 object and what I am assuming is the name of the function, looks like a method on the person1 object using dot notation. Can anyone explain how this works?
The line
person1.getFullName = ...
is a normal assignment statement. It assigns the value on the right hand side to the property getFullName of the object in person1. If the property doesn't exist yet it will be created.
Functions are values (objects) like any other in JavaScript and thus they can be used everywhere were a value is expected.
So yes, person1.getFullName will contain a function and it can be called like any other function: person1.getFullName().
Objects have properties.
Properties have values.
Functions are a value.
If the value of a property is a function then we call that a method.
That's all there is to it.
function Person(fName, lName) {
this.firstName = fName
this.lastName = lName
}
const person1 = new Person("Bruce", "Wayne")
const person2 = new Person("Bat", "Man")
person1.getFullName = function () {
return this.firstName + ' ' + this.lastName
}
console.log(person1.getFullName())
Basically a new property called getFullName is created for the object person1. This new property is defined to return the first name and the lastname of the person1 object. So when you call console.log(person1.getFullName()) this will print the firstname and the lastname of the person1.
So far I saw three ways for creating an object in JavaScript. Which way is best for creating an object and why?
I also saw that in all of these examples the keyword var is not used before a property — why? Is it not necessary to declare var before the name of a property as it mentioned that properties are variables?
In the second and third way, the name of the object is in upper-case whereas in the first way the name of the object is in lower-case. What case should we use for an object name?
First way:
function person(fname, lname, age, eyecolor){
this.firstname = fname;
this.lastname = lname;
this.age = age;
this.eyecolor = eyecolor;
}
myFather = new person("John", "Doe", 50, "blue");
document.write(myFather.firstname + " is " + myFather.age + " years old.");
Second way:
var Robot = {
metal: "Titanium",
killAllHumans: function(){
alert("Exterminate!");
}
};
Robot.killAllHumans();
Third way — JavaScript objects using array syntax:
var NewObject = {};
NewObject['property1'] = value;
NewObject['property2'] = value;
NewObject['method'] = function(){ /* function code here */ }
There is no best way, it depends on your use case.
Use way 1 if you want to create several similar objects. In your example, Person (you should start the name with a capital letter) is called the constructor function. This is similar to classes in other OO languages.
Use way 2 if you only need one object of a kind (like a singleton). If you want this object to inherit from another one, then you have to use a constructor function though.
Use way 3 if you want to initialize properties of the object depending on other properties of it or if you have dynamic property names.
Update: As requested examples for the third way.
Dependent properties:
The following does not work as this does not refer to book. There is no way to initialize a property with values of other properties in a object literal:
var book = {
price: somePrice * discount,
pages: 500,
pricePerPage: this.price / this.pages
};
instead, you could do:
var book = {
price: somePrice * discount,
pages: 500
};
book.pricePerPage = book.price / book.pages;
// or book['pricePerPage'] = book.price / book.pages;
Dynamic property names:
If the property name is stored in some variable or created through some expression, then you have to use bracket notation:
var name = 'propertyName';
// the property will be `name`, not `propertyName`
var obj = {
name: 42
};
// same here
obj.name = 42;
// this works, it will set `propertyName`
obj[name] = 42;
There is various way to define a function. It is totally based upon your requirement. Below are the few styles :-
Object Constructor
Literal constructor
Function Based
Protoype Based
Function and Prototype Based
Singleton Based
Examples:
Object constructor
var person = new Object();
person.name = "Anand",
person.getName = function(){
return this.name ;
};
Literal constructor
var person = {
name : "Anand",
getName : function (){
return this.name
}
}
function Constructor
function Person(name){
this.name = name
this.getName = function(){
return this.name
}
}
Prototype
function Person(){};
Person.prototype.name = "Anand";
Function/Prototype combination
function Person(name){
this.name = name;
}
Person.prototype.getName = function(){
return this.name
}
Singleton
var person = new function(){
this.name = "Anand"
}
You can try it on console, if you have any confusion.
There is no "best way" to create an object. Each way has benefits depending on your use case.
The constructor pattern (a function paired with the new operator to invoke it) provides the possibility of using prototypal inheritance, whereas the other ways don't. So if you want prototypal inheritance, then a constructor function is a fine way to go.
However, if you want prototypal inheritance, you may as well use Object.create, which makes the inheritance more obvious.
Creating an object literal (ex: var obj = {foo: "bar"};) works great if you happen to have all the properties you wish to set on hand at creation time.
For setting properties later, the NewObject.property1 syntax is generally preferable to NewObject['property1'] if you know the property name. But the latter is useful when you don't actually have the property's name ahead of time (ex: NewObject[someStringVar]).
Hope this helps!
I guess it depends on what you want. For simple objects, I guess you could use the second methods. When your objects grow larger and you're planning on using similar objects, I guess the first method would be better. That way you can also extend it using prototypes.
Example:
function Circle(radius) {
this.radius = radius;
}
Circle.prototype.getCircumference = function() {
return Math.PI * 2 * this.radius;
};
Circle.prototype.getArea = function() {
return Math.PI * this.radius * this.radius;
}
I am not a big fan of the third method, but it's really useful for dynamically editing properties, for example var foo='bar'; var bar = someObject[foo];.
There are a many ways to create your objects in JavaScript.
Using a constructer function to create an object or object literal notation is using alot in JavaScript. Also creating an instance of Object and then adding properties and methods to it, there are three common ways to do create objects in JavaScript.
Constructer functions
There are built-in constructer functions that we all may use them time to time, like Date(), Number(), Boolean() etc, all constructer functions start with Capital letter, in the meantime we can create custom constructor function in JavaScript like this:
function Box (Width, Height, fill) {
this.width = Width; // The width of the box
this.height = Height; // The height of the box
this.fill = true; // Is it filled or not?
}
and you can invoke it, simply using new(), to create a new instance of the constructor, create something like below and call the constructor function with filled parameters:
var newBox = new Box(8, 12, true);
Object literals
Using object literals are very used case creating object in JavaScript, this an example of creating a simple object, you can assign anything to your object properties as long as they are defined:
var person = {
name: "Alireza",
surname: "Dezfoolian"
nose: 1,
feet: 2,
hands: 2,
cash: null
};
Prototyping
After creating an Object, you can prototype more members to that, for example adding colour to our Box, we can do this:
Box.prototype.colour = 'red';
While many people here say there is no best way for object creation, there is a rationale as to why there are so many ways to create objects in JavaScript, as of 2019, and this has to do with the progress of JavaScript over the different iterations of EcmaScript releases dating back to 1997.
Prior to ECMAScript 5, there were only two ways of creating objects: the constructor function or the literal notation ( a better alternative to new Object()). With the constructor function notation you create an object that can be instantiated into multiple instances (with the new keyword), while the literal notation delivers a single object, like a singleton.
// constructor function
function Person() {};
// literal notation
var Person = {};
Regardless of the method you use, JavaScript objects are simply properties of key value pairs:
// Method 1: dot notation
obj.firstName = 'Bob';
// Method 2: bracket notation. With bracket notation, you can use invalid characters for a javascript identifier.
obj['lastName'] = 'Smith';
// Method 3: Object.defineProperty
Object.defineProperty(obj, 'firstName', {
value: 'Bob',
writable: true,
configurable: true,
enumerable: false
})
// Method 4: Object.defineProperties
Object.defineProperties(obj, {
firstName: {
value: 'Bob',
writable: true
},
lastName: {
value: 'Smith',
writable: false
}
});
In early versions of JavaScript, the only real way to mimic class-based inheritance was to use constructor functions. the constructor function is a special function that is invoked with the 'new' keyword. By convention, the function identifier is capitalized, albiet it is not required. Inside of the constructor, we refer to the 'this' keyword to add properties to the object that the constructor function is implicitly creating. The constructor function implicitly returns the new object with the populated properties back to the calling function implicitly, unless you explicitly use the return keyword and return something else.
function Person(firstName, lastName) {
this.firstName = firstName;
this.lastName = lastName;
this.sayName = function(){
return "My name is " + this.firstName + " " + this.lastName;
}
}
var bob = new Person("Bob", "Smith");
bob instanceOf Person // true
There is a problem with the sayName method. Typically, in Object-Oriented Class-based programming languages, you use classes as factories to create objects. Each object will have its own instance variables, but it will have a pointer to the methods defined in the class blueprint. Unfortunately, when using JavaScript's constructor function, every time it is called, it will define a new sayName property on the newly created object. So each object will have its own unique sayName property. This will consume more memory resources.
In addition to increased memory resources, defining methods inside of the constructor function eliminates the possibility of inheritance. Again, the method will be defined as a property on the newly created object and no other object, so inheritance cannot work like. Hence, JavaScript provides the prototype chain as a form of inheritance, making JavaScript a prototypal language.
If you have a parent and a parent shares many properties of a child, then the child should inherit those properties. Prior to ES5, it was accomplished as follows:
function Parent(eyeColor, hairColor) {
this.eyeColor = eyeColor;
this.hairColor = hairColor;
}
Parent.prototype.getEyeColor = function() {
console.log('has ' + this.eyeColor);
}
Parent.prototype.getHairColor = function() {
console.log('has ' + this.hairColor);
}
function Child(firstName, lastName) {
Parent.call(this, arguments[2], arguments[3]);
this.firstName = firstName;
this.lastName = lastName;
}
Child.prototype = Parent.prototype;
var child = new Child('Bob', 'Smith', 'blue', 'blonde');
child.getEyeColor(); // has blue eyes
child.getHairColor(); // has blonde hair
The way we utilized the prototype chain above has a quirk. Since the prototype is a live link, by changing the property of one object in the prototype chain, you'd be changing same property of another object as well. Obviously, changing a child's inherited method should not change the parent's method. Object.create resolved this issue by using a polyfill. Thus, with Object.create, you can safely modify a child's property in the prototype chain without affecting the parent's same property in the prototype chain.
ECMAScript 5 introduced Object.create to solve the aforementioned bug in the constructor function for object creation. The Object.create() method CREATES a new object, using an existing object as the prototype of the newly created object. Since a new object is created, you no longer have the issue where modifying the child property in the prototype chain will modify the parent's reference to that property in the chain.
var bobSmith = {
firstName: "Bob",
lastName: "Smith",
sayName: function(){
return "My name is " + this.firstName + " " + this.lastName;
}
}
var janeSmith = Object.create(bobSmith, {
firstName : { value: "Jane" }
})
console.log(bobSmith.sayName()); // My name is Bob Smith
console.log(janeSmith.sayName()); // My name is Jane Smith
janeSmith.__proto__ == bobSmith; // true
janeSmith instanceof bobSmith; // Uncaught TypeError: Right-hand side of 'instanceof' is not callable. Error occurs because bobSmith is not a constructor function.
Prior to ES6, here was a common creational pattern to utilize function constructors and Object.create:
const View = function(element){
this.element = element;
}
View.prototype = {
getElement: function(){
this.element
}
}
const SubView = function(element){
View.call(this, element);
}
SubView.prototype = Object.create(View.prototype);
Now Object.create coupled with constructor functions have been widely used for object creation and inheritance in JavaScript. However, ES6 introduced the concept of classes, which are primarily syntactical sugar over JavaScript's existing prototype-based inheritance. The class syntax does not introduce a new object-oriented inheritance model to JavaScript. Thus, JavaScript remains a prototypal language.
ES6 classes make inheritance much easier. We no longer have to manually copy the parent class's prototype functions and reset the child class's constructor.
// create parent class
class Person {
constructor (name) {
this.name = name;
}
}
// create child class and extend our parent class
class Boy extends Person {
constructor (name, color) {
// invoke our parent constructor function passing in any required parameters
super(name);
this.favoriteColor = color;
}
}
const boy = new Boy('bob', 'blue')
boy.favoriteColor; // blue
All in all, these 5 different strategies of Object Creation in JavaScript coincided the evolution of the EcmaScript standard.
Of course there is a best way.Objects in javascript have enumerable and nonenumerable properties.
var empty = {};
console.log(empty.toString);
// . function toString(){...}
console.log(empty.toString());
// . [object Object]
In the example above you can see that an empty object actually has properties.
Ok first let's see which is the best way:
var new_object = Object.create(null)
new_object.name = 'Roland'
new_object.last_name = 'Doda'
//etc
console.log("toString" in new_object) //=> false
In the example above the log will output false.
Now let's see why the other object creation ways are incorrect.
//Object constructor
var object = new Object();
console.log("toString" in object); //=> true
//Literal constructor
var person = {
name : "Anand",
getName : function (){
return this.name
}
}
console.log("toString" in person); //=> true
//function Constructor
function Person(name){
this.name = name
this.getName = function(){
return this.name
}
}
var person = new Person ('landi')
console.log("toString" in person); //=> true
//Prototype
function Person(){};
Person.prototype.name = "Anand";
console.log("toString" in person); //=> true
//Function/Prototype combination
function Person2(name){
this.name = name;
}
Person2.prototype.getName = function(){
return this.name
}
var person2 = new Person2('Roland')
console.log("toString" in person2) //=> true
As you can see above,all examples log true.Which means if you have a case that you have a for in loop to see if the object has a property will lead you to wrong results probably.
Note that the best way it is not easy.You have to define all properties of object line by line.The other ways are more easier and will have less code to create an object but you have to be aware in some cases.
I always use the "other ways" by the way and one solution to above warning if you don't use the best way is:
for (var property in new_object) {
if (new_object.hasOwnProperty(property)) {
// ... this is an own property
}
}
Majorly there are 3 ways of creating Objects-
Simplest one is using object literals.
const myObject = {}
Though this method is the simplest but has a disadvantage i.e if your object has behaviour(functions in it),then in future if you want to make any changes to it you would have to change it in all the objects.
So in that case it is better to use Factory or Constructor Functions.(anyone that you like)
Factory Functions are those functions that return an object.e.g-
function factoryFunc(exampleValue){
return{
exampleProperty: exampleValue
}
}
Constructor Functions are those functions that assign properties to objects using "this" keyword.e.g-
function constructorFunc(exampleValue){
this.exampleProperty= exampleValue;
}
const myObj= new constructorFunc(1);
I want to check my idea is correct or not?
Codes:
function Person(firstname, lastname) {
this.firstname = firstname;
this.lastname = lastname;
}
Person.prototype.getFullName = function () {
return this.firstname + ' ' + this.lastname;
}
var john = new Person('Melo','Tang');
I call the code in the following picture "function constructor".
function Person(firstname, lastname) {
this.firstname = firstname;
this.lastname = lastname;
}
When the program run to this line
var john = new Person('Melo','Tang');
JS will use prototype chain to add the getFullName function in the "function constructor" Object and new a empty Object like following picture am I right?
I don't really understand what your diagram or the arrows or their colors are supposed to represent.
When the program runs to this line
var john = new Person('Melo','Tang');
What happens here is exactly that a new object is constructed via the Person constructor, with Person.prototype as its prototype. Other than being used as the prototype for the new object, Person.prototype is not examined or consulted, nor is anything done with the methods on it at this time. The prototype is consulted only when looking up properties and methods, such as when calling john.getFullName().
For clarity, I would avoid the term "function constructor object". Just call it a "constructor (function)".
This question already has answers here:
How does JavaScript .prototype work?
(26 answers)
Closed 6 years ago.
I'm trying to understand JavaScript prototype and when I attempted coding this I get an error:
function Person(firstname, last name) {
this.firstname = firstname;
this.lastname = lastname;
}
var A = new Person('John', 'Doe');
A.prototype.name = 'Toby';
I get an error stating cannot set property 'name' of undefined. Can't i assign a property on it's prototype of Object A. This is just a simple exercise to get an understanding of prototypes
Objects don't have a prototype property (unless you create one). You usually only assign to the prototype property of constructors:
function Person(firstname, lastname) {
this.firstname = firstname;
this.lastname = lastname;
}
Person.prototype.name = 'Toby';
var A = new Person('John', 'Doe');
// A.name === 'Toby';
So far I saw three ways for creating an object in JavaScript. Which way is best for creating an object and why?
I also saw that in all of these examples the keyword var is not used before a property — why? Is it not necessary to declare var before the name of a property as it mentioned that properties are variables?
In the second and third way, the name of the object is in upper-case whereas in the first way the name of the object is in lower-case. What case should we use for an object name?
First way:
function person(fname, lname, age, eyecolor){
this.firstname = fname;
this.lastname = lname;
this.age = age;
this.eyecolor = eyecolor;
}
myFather = new person("John", "Doe", 50, "blue");
document.write(myFather.firstname + " is " + myFather.age + " years old.");
Second way:
var Robot = {
metal: "Titanium",
killAllHumans: function(){
alert("Exterminate!");
}
};
Robot.killAllHumans();
Third way — JavaScript objects using array syntax:
var NewObject = {};
NewObject['property1'] = value;
NewObject['property2'] = value;
NewObject['method'] = function(){ /* function code here */ }
There is no best way, it depends on your use case.
Use way 1 if you want to create several similar objects. In your example, Person (you should start the name with a capital letter) is called the constructor function. This is similar to classes in other OO languages.
Use way 2 if you only need one object of a kind (like a singleton). If you want this object to inherit from another one, then you have to use a constructor function though.
Use way 3 if you want to initialize properties of the object depending on other properties of it or if you have dynamic property names.
Update: As requested examples for the third way.
Dependent properties:
The following does not work as this does not refer to book. There is no way to initialize a property with values of other properties in a object literal:
var book = {
price: somePrice * discount,
pages: 500,
pricePerPage: this.price / this.pages
};
instead, you could do:
var book = {
price: somePrice * discount,
pages: 500
};
book.pricePerPage = book.price / book.pages;
// or book['pricePerPage'] = book.price / book.pages;
Dynamic property names:
If the property name is stored in some variable or created through some expression, then you have to use bracket notation:
var name = 'propertyName';
// the property will be `name`, not `propertyName`
var obj = {
name: 42
};
// same here
obj.name = 42;
// this works, it will set `propertyName`
obj[name] = 42;
There is various way to define a function. It is totally based upon your requirement. Below are the few styles :-
Object Constructor
Literal constructor
Function Based
Protoype Based
Function and Prototype Based
Singleton Based
Examples:
Object constructor
var person = new Object();
person.name = "Anand",
person.getName = function(){
return this.name ;
};
Literal constructor
var person = {
name : "Anand",
getName : function (){
return this.name
}
}
function Constructor
function Person(name){
this.name = name
this.getName = function(){
return this.name
}
}
Prototype
function Person(){};
Person.prototype.name = "Anand";
Function/Prototype combination
function Person(name){
this.name = name;
}
Person.prototype.getName = function(){
return this.name
}
Singleton
var person = new function(){
this.name = "Anand"
}
You can try it on console, if you have any confusion.
There is no "best way" to create an object. Each way has benefits depending on your use case.
The constructor pattern (a function paired with the new operator to invoke it) provides the possibility of using prototypal inheritance, whereas the other ways don't. So if you want prototypal inheritance, then a constructor function is a fine way to go.
However, if you want prototypal inheritance, you may as well use Object.create, which makes the inheritance more obvious.
Creating an object literal (ex: var obj = {foo: "bar"};) works great if you happen to have all the properties you wish to set on hand at creation time.
For setting properties later, the NewObject.property1 syntax is generally preferable to NewObject['property1'] if you know the property name. But the latter is useful when you don't actually have the property's name ahead of time (ex: NewObject[someStringVar]).
Hope this helps!
I guess it depends on what you want. For simple objects, I guess you could use the second methods. When your objects grow larger and you're planning on using similar objects, I guess the first method would be better. That way you can also extend it using prototypes.
Example:
function Circle(radius) {
this.radius = radius;
}
Circle.prototype.getCircumference = function() {
return Math.PI * 2 * this.radius;
};
Circle.prototype.getArea = function() {
return Math.PI * this.radius * this.radius;
}
I am not a big fan of the third method, but it's really useful for dynamically editing properties, for example var foo='bar'; var bar = someObject[foo];.
There are a many ways to create your objects in JavaScript.
Using a constructer function to create an object or object literal notation is using alot in JavaScript. Also creating an instance of Object and then adding properties and methods to it, there are three common ways to do create objects in JavaScript.
Constructer functions
There are built-in constructer functions that we all may use them time to time, like Date(), Number(), Boolean() etc, all constructer functions start with Capital letter, in the meantime we can create custom constructor function in JavaScript like this:
function Box (Width, Height, fill) {
this.width = Width; // The width of the box
this.height = Height; // The height of the box
this.fill = true; // Is it filled or not?
}
and you can invoke it, simply using new(), to create a new instance of the constructor, create something like below and call the constructor function with filled parameters:
var newBox = new Box(8, 12, true);
Object literals
Using object literals are very used case creating object in JavaScript, this an example of creating a simple object, you can assign anything to your object properties as long as they are defined:
var person = {
name: "Alireza",
surname: "Dezfoolian"
nose: 1,
feet: 2,
hands: 2,
cash: null
};
Prototyping
After creating an Object, you can prototype more members to that, for example adding colour to our Box, we can do this:
Box.prototype.colour = 'red';
While many people here say there is no best way for object creation, there is a rationale as to why there are so many ways to create objects in JavaScript, as of 2019, and this has to do with the progress of JavaScript over the different iterations of EcmaScript releases dating back to 1997.
Prior to ECMAScript 5, there were only two ways of creating objects: the constructor function or the literal notation ( a better alternative to new Object()). With the constructor function notation you create an object that can be instantiated into multiple instances (with the new keyword), while the literal notation delivers a single object, like a singleton.
// constructor function
function Person() {};
// literal notation
var Person = {};
Regardless of the method you use, JavaScript objects are simply properties of key value pairs:
// Method 1: dot notation
obj.firstName = 'Bob';
// Method 2: bracket notation. With bracket notation, you can use invalid characters for a javascript identifier.
obj['lastName'] = 'Smith';
// Method 3: Object.defineProperty
Object.defineProperty(obj, 'firstName', {
value: 'Bob',
writable: true,
configurable: true,
enumerable: false
})
// Method 4: Object.defineProperties
Object.defineProperties(obj, {
firstName: {
value: 'Bob',
writable: true
},
lastName: {
value: 'Smith',
writable: false
}
});
In early versions of JavaScript, the only real way to mimic class-based inheritance was to use constructor functions. the constructor function is a special function that is invoked with the 'new' keyword. By convention, the function identifier is capitalized, albiet it is not required. Inside of the constructor, we refer to the 'this' keyword to add properties to the object that the constructor function is implicitly creating. The constructor function implicitly returns the new object with the populated properties back to the calling function implicitly, unless you explicitly use the return keyword and return something else.
function Person(firstName, lastName) {
this.firstName = firstName;
this.lastName = lastName;
this.sayName = function(){
return "My name is " + this.firstName + " " + this.lastName;
}
}
var bob = new Person("Bob", "Smith");
bob instanceOf Person // true
There is a problem with the sayName method. Typically, in Object-Oriented Class-based programming languages, you use classes as factories to create objects. Each object will have its own instance variables, but it will have a pointer to the methods defined in the class blueprint. Unfortunately, when using JavaScript's constructor function, every time it is called, it will define a new sayName property on the newly created object. So each object will have its own unique sayName property. This will consume more memory resources.
In addition to increased memory resources, defining methods inside of the constructor function eliminates the possibility of inheritance. Again, the method will be defined as a property on the newly created object and no other object, so inheritance cannot work like. Hence, JavaScript provides the prototype chain as a form of inheritance, making JavaScript a prototypal language.
If you have a parent and a parent shares many properties of a child, then the child should inherit those properties. Prior to ES5, it was accomplished as follows:
function Parent(eyeColor, hairColor) {
this.eyeColor = eyeColor;
this.hairColor = hairColor;
}
Parent.prototype.getEyeColor = function() {
console.log('has ' + this.eyeColor);
}
Parent.prototype.getHairColor = function() {
console.log('has ' + this.hairColor);
}
function Child(firstName, lastName) {
Parent.call(this, arguments[2], arguments[3]);
this.firstName = firstName;
this.lastName = lastName;
}
Child.prototype = Parent.prototype;
var child = new Child('Bob', 'Smith', 'blue', 'blonde');
child.getEyeColor(); // has blue eyes
child.getHairColor(); // has blonde hair
The way we utilized the prototype chain above has a quirk. Since the prototype is a live link, by changing the property of one object in the prototype chain, you'd be changing same property of another object as well. Obviously, changing a child's inherited method should not change the parent's method. Object.create resolved this issue by using a polyfill. Thus, with Object.create, you can safely modify a child's property in the prototype chain without affecting the parent's same property in the prototype chain.
ECMAScript 5 introduced Object.create to solve the aforementioned bug in the constructor function for object creation. The Object.create() method CREATES a new object, using an existing object as the prototype of the newly created object. Since a new object is created, you no longer have the issue where modifying the child property in the prototype chain will modify the parent's reference to that property in the chain.
var bobSmith = {
firstName: "Bob",
lastName: "Smith",
sayName: function(){
return "My name is " + this.firstName + " " + this.lastName;
}
}
var janeSmith = Object.create(bobSmith, {
firstName : { value: "Jane" }
})
console.log(bobSmith.sayName()); // My name is Bob Smith
console.log(janeSmith.sayName()); // My name is Jane Smith
janeSmith.__proto__ == bobSmith; // true
janeSmith instanceof bobSmith; // Uncaught TypeError: Right-hand side of 'instanceof' is not callable. Error occurs because bobSmith is not a constructor function.
Prior to ES6, here was a common creational pattern to utilize function constructors and Object.create:
const View = function(element){
this.element = element;
}
View.prototype = {
getElement: function(){
this.element
}
}
const SubView = function(element){
View.call(this, element);
}
SubView.prototype = Object.create(View.prototype);
Now Object.create coupled with constructor functions have been widely used for object creation and inheritance in JavaScript. However, ES6 introduced the concept of classes, which are primarily syntactical sugar over JavaScript's existing prototype-based inheritance. The class syntax does not introduce a new object-oriented inheritance model to JavaScript. Thus, JavaScript remains a prototypal language.
ES6 classes make inheritance much easier. We no longer have to manually copy the parent class's prototype functions and reset the child class's constructor.
// create parent class
class Person {
constructor (name) {
this.name = name;
}
}
// create child class and extend our parent class
class Boy extends Person {
constructor (name, color) {
// invoke our parent constructor function passing in any required parameters
super(name);
this.favoriteColor = color;
}
}
const boy = new Boy('bob', 'blue')
boy.favoriteColor; // blue
All in all, these 5 different strategies of Object Creation in JavaScript coincided the evolution of the EcmaScript standard.
Of course there is a best way.Objects in javascript have enumerable and nonenumerable properties.
var empty = {};
console.log(empty.toString);
// . function toString(){...}
console.log(empty.toString());
// . [object Object]
In the example above you can see that an empty object actually has properties.
Ok first let's see which is the best way:
var new_object = Object.create(null)
new_object.name = 'Roland'
new_object.last_name = 'Doda'
//etc
console.log("toString" in new_object) //=> false
In the example above the log will output false.
Now let's see why the other object creation ways are incorrect.
//Object constructor
var object = new Object();
console.log("toString" in object); //=> true
//Literal constructor
var person = {
name : "Anand",
getName : function (){
return this.name
}
}
console.log("toString" in person); //=> true
//function Constructor
function Person(name){
this.name = name
this.getName = function(){
return this.name
}
}
var person = new Person ('landi')
console.log("toString" in person); //=> true
//Prototype
function Person(){};
Person.prototype.name = "Anand";
console.log("toString" in person); //=> true
//Function/Prototype combination
function Person2(name){
this.name = name;
}
Person2.prototype.getName = function(){
return this.name
}
var person2 = new Person2('Roland')
console.log("toString" in person2) //=> true
As you can see above,all examples log true.Which means if you have a case that you have a for in loop to see if the object has a property will lead you to wrong results probably.
Note that the best way it is not easy.You have to define all properties of object line by line.The other ways are more easier and will have less code to create an object but you have to be aware in some cases.
I always use the "other ways" by the way and one solution to above warning if you don't use the best way is:
for (var property in new_object) {
if (new_object.hasOwnProperty(property)) {
// ... this is an own property
}
}
Majorly there are 3 ways of creating Objects-
Simplest one is using object literals.
const myObject = {}
Though this method is the simplest but has a disadvantage i.e if your object has behaviour(functions in it),then in future if you want to make any changes to it you would have to change it in all the objects.
So in that case it is better to use Factory or Constructor Functions.(anyone that you like)
Factory Functions are those functions that return an object.e.g-
function factoryFunc(exampleValue){
return{
exampleProperty: exampleValue
}
}
Constructor Functions are those functions that assign properties to objects using "this" keyword.e.g-
function constructorFunc(exampleValue){
this.exampleProperty= exampleValue;
}
const myObj= new constructorFunc(1);