I have a Dog Constructor as follows:
var Dog = function(name,type)
{
this.name = name;
this.type = type;
this.normalObjFunc = function()
{
this.name = "kl";
}
var retfunc = function()
{
return this.name;
}
return retfunc;
}
In the retfunc function() , I am trying to access this.name in the following way.
var dogObj = new Dog("hj","labrador");
alert(dogObj());
In the output , I get as "result" in the alert messageBox, I am not getting what does the o/p "result" ,means?
I have purposely not included retfunc to "this" object, does it mean I cant access this.name inside retfunc() because a SEparate "this" would be created?
I am also aware of the fact that assigning var self =this solves the problem.
I just want to know what is "result" which is the output and why not undefined ideally?
The issue is because the scope of this within the functions will be the window. You need to cache the object reference in a variable and call that, like this:
var Dog = function(name, type) {
var _this = this;
this.name = name;
this.type = type;
this.normalObjFunc = function() {
_this.name = "kl";
}
var retfunc = function() {
return _this.name;
}
return retfunc;
}
var dogObj = new Dog("hj", "labrador");
console.log(dogObj());
Alternatively you can prototype the functions to keep the scope of this, however you would need to change your logic as it means that the return value of Dog() could not be the function.
var Dog = function(name, type) {
this.name = name;
this.type = type;
}
Dog.prototype.normalObjFunc = function() {
this.name = "kl";
}
Dog.prototype.retfunc = function() {
return this.name;
}
var dogObj = new Dog("hj", "labrador");
console.log(dogObj.retfunc());
Related
What am I trying to do is as following:
var Person = function(name) {
this.name = name;
}
Person.prototype.getName = function () {
return this.name;
}
// This will return error;
console.log(Person('John').getName());
// While this won't.
var p1 = new Person('john');
console.log(p1.getName());
Am I misunderstanding something?
// This will return error;
console.log(Person('John').getName());
it returns an error bcoz Person() by default returns undefined ,but if you use new it will return the newly created object.
// While this won't.
var p1 = new Person('john');
console.log(p1.getName());
this works bcoz a new object with __proto__ set to Person.prototype is returned and since there is a getName() on it , it works as expected.
you may use scope safe constructor for your constructor to work without explicit new.
function Person(name) {
if(this instanceof Person) {
this.name = name;
} else {
return new Person(name);
}
}
http://www.mikepackdev.com/blog_posts/9-new-scope-safe-constructors-in-oo-javascript
If you don't want to have the new keyword all over your code (and I can't think of a good reason to want that, you would be basically hiding an important information), you could just do something like:
var pPerson = function(name) {
this.name = name;
};
pPerson.prototype.getName = function () {
return this.name;
};
var Person = function (name) {
return new pPerson(name);
};
You can use Object.create() if you don't want to use the new keyword. Here's an example from MDN:
// Animal properties and method encapsulation
var Animal = {
type: "Invertebrates", // Default value of properties
displayType : function(){ // Method which will display type of Animal
console.log(this.type);
}
}
// Create new animal type called animal1
var animal1 = Object.create(Animal);
animal1.displayType(); // Output:Invertebrates
// Create new animal type called Fishes
var fish = Object.create(Animal);
fish.type = "Fishes";
fish.displayType(); // Output:Fishes
If you really really hate your self, you can do this
var Person = function(name) {
var This = {};
This.name = name;
//See note
Object.setPrototypeOf(This, arguments.callee.prototype);
return This;
}
Person.prototype.getName = function () {
return this.name;
}
var p = Person('John');
console.log(p.getName());
Note
You absolutely have to read about this.
You can try creating prototype functions as a part of parent function itself.
var Person = function(name) {
this.name = name;
this.get_name = function() {
return this.name;
}
return this;
}
Person.prototype.getName = function() {
return this.name;
}
// This will return error;
console.log(Person('John').get_name());
// While this won't.
var p1 = new Person('john');
console.log(p1.getName());
I have created a simple object that want to use as a blueprint for other objects. But something is not going well. Can anyone find out why? When I click one button it should change innerHTML of the div to display the properties of the new objects!
here is a fiddle
var objekt = {
name : "olsi",
surname : "Angjellari",
kot : function () {
return this.name + this.surname
},
print : function () {
id.innerHTML = this.kot()
}
};
http://jsfiddle.net/cTRuL/
There are a number of problems:
When you want to do:
var dana = new objekt();
Then, objekt must be a function, not just an object because an object is not a constructor, only a function can be a constructor. This is one way to do that:
function objekt() {
this.name = "olsi";
this.surname = "Angjellari";
};
objekt.prototype = {
kot : function () {
return this.name + this.surname
},
print : function () {
id.innerHTML = this.kot()
}
};
Second, in your jsFiddle if you're going to put function names in the HTML, then those functions have to be global. To make your code global in the jsFiddle, you have to set the upper left setting to "No wrap - in <body>" or "No wrap - in <head>". As you had your jsFiddle, your code was defined inside an onload handler and therefore NOT reachable by function calls from your HTML.
Third, once you make objekt into a function to fix the previous issue, then you can't call objekt.print() directly. You probably want to call .print on an actual object of type objekt like dana or boi.
You can see it all working here: http://jsfiddle.net/jfriend00/7TbEx/
you want to create a constructor so you can make instances using the new operator like you are trying
function objekt(name,surname){
this.name = name||"olsi";
this.surname = surname||"Angjellari";
this.kot = function () {
return this.name + this.surname
};
this.print = function () {
id.innerHTML = this.kot()
};
}
var obj = new objekt();
var obj2 = new objekt("First","Last");
obj.print();
obj2.print();
You could also make these through the prototype
function objekt(){}
objekt.prototype.name = "";
objekt.prototype.surname = "";
objekt.prototype.kot = function(){
return this.name + this.surname;
};
objekt.prototype.kot = function(){
id.innerHTML = this.kot();
};
var obj = new objekt();
obj.name = "First";
obj.surname = "Last";
var obj2 = new objekt();
obj2.name = "Last";
obj2.surname = "First";
obj.print();
obj2.print();
$(document).ready(function () {
var patient = (function (options) {
var age = options.age;
var name = options.name;
function getName() {
return this.name;
}
function setName(val) {
name = val;
}
function getAge() {
return this.age;
}
function setAge(val) {
age = val;
}
return {
getAge: getAge,
setAge: setAge,
getName: getName,
setName: setName
}
})();
});
I realize that I'm never passing any options in my example here.
If I try to do something like patient.setAge('100') and then console.log(patient.getAge()) I get an error saying cannot read property Age of undefined. The overarching theme that I'm trying to get at is within a module, how can I emulate consturctors to instantiate a new patient object while keeping all the OOP goodness of private variables and all that jazz.
I've seen some examples of constructors in a module pattern on here and I haven't understood them very well. Is it a good idea in general to have a constructor in a module? Is its main purpose similarity with class-based languages?
This is a constructor:
function Patient(options) {
options = options || {};
this.age = options.age;
this.name = options.name;
}
$(document).ready(function () {
var patient = new Patient();
});
You can put it inside a module if you want. What you shouldn’t do is provide getters and setters, especially ones that don’t do anything. If you’re exposing a variable through two properties to get and set it, it should just be one property.
Try this
function Patient (options) {
options = options || {};
var age = options.age;
var name = options.name;
function getName() {
return name;
}
function setName(val) {
name = val;
}
function getAge() {
return age;
}
function setAge(val) {
age = val;
}
return {
getAge: getAge,
setAge: setAge,
getName: getName,
setName: setName
}
}); // pass empty object
$(document).ready(function () {
var p1 = new Patient({});
var p2 = new Patient();
var p3 = new Patient({age:20});
var p4 = new Patient({name:"abcd"});
var p5 = new Patient({age:21, name:"abcd"});
});
Is it possible to define an object within another object? I'm thinking something like this:
function MyObj(name) {
this.name = name;
function EmbeddedObj(id) {
this.id = id;
}
}
And I could then create an EmbeddedObj like this:
var myEmbeddedObj = new MyObj.EmbeddedObj();
Meme for bonus points: Objectception! :o
Yes, and no.
function MyObj(name) {
this.name = name;
}
MyObj.EmbeddedObj = function EmbeddedObj(id) {
this.id = id;
}
new MyObj.EmbeddedObj(42);
Would run, but it might not yield the expected results for "embedded object" (see comment).
Note that in the case of new expr the expression is evaluated first so, in this case it creates a new object using the function-object evaluated from MyObject.EmbeddedObj as a constructor. (There is a silly rule with parenthesis in the expression, but that's another story.)
Now, if a "parent" and "child" relationship was desired, that could be done, using a more round-about method:
function Parent (name) {
this.name = name;
var parent = this; // for closure
this.Child = function Child () {
this.Parent = parent;
}
}
// create new parent object
var parent = new Parent();
// each new parent has a different Child constructor and
// any function-object can be used as a constructor
var child = new parent.Child();
// true: child is "bound" to parent
child.Parent === parent;
function MyObj(name) {
this.name = name;
}
MyObj.EmbeddedObj = function(id) {
this.id = id;
}
var myEmbeddedObj = new MyObj.EmbeddedObj();
Does that look like what you're after?
Here is example of nested constructor.
function cimdb(name,review,year) {
function nestedConstructor(name,review,year) {
this.name = name;
this.review = review;
this.year = year
};
this.name = name;
this[name] = new nestedConstructor(name,review,year);
}
var lionking = new cimdb("The Lion King", "The lion King review ..", 2015);
I guess this is what you mean by nested object constructor.
The easiest way to nest other objects in a constructor is to create its field and then create a new object when invoking the constructor. Below is an example:
function Product(name, price, category, producer) {
this.name = name;
this.price = price;
this.category = category;
// nested constructor
this.producer = producer;
}
function Producer(contributor, address) {
this.contributor = contributor;
this.address = address;
}
let prod1 = new Product("Milk", 2.5, "Dairy", new Producer("Nestle", "Warszawa"));
Not sure what I'm doing wrong here, I just want to be able to have functions of an object reference the object scope
myscipt.js
function MyFoo () {
this.name = 'myname';
}
function MyBar () {
this.myFoo = new MyFoo();
function setMyFoosName( name ) {
this.myFoo.name = name;
}
}
somepage.html
<scipt>
$('document').ready( function() {
$.myBar = new MyBar();
}
...
some action
...
$.myBar.setMyFoosName( 'new name' );
</script>
this throws an exception:
this.myFoo.name = name; this.myFoo is not defined
Lekensteyn and Ken got it half right each.
You have to put "this" in a variable, like Lekensteyn did, in order to be able to reference it inside of the nested function as well.
You have to make setMyFoosName accessible outside of the scope of MyBar, by assigning it to a property of "this", like Ken did.
This is how I would do it:
function MyFoo () {
this.name = 'myname';
}
function MyBar () {
var that = this;
this.myFoo = new MyFoo();
this.setMyFoosName = function( name ) {
that.myFoo.name = name;
}
}
Cant you do an instance static method with the JSON Data type?
var MyFoo = {
_instance : null,
Instance : function(){
if(this._instance == null)
{
this._instance = new this.Object();
}
return this._instance;
},
Object : function()
{
this.name = 'not robert';
}
}
function MyBar (){
this.setMyFoosName = function ( name ) {
MyFoo.Instance().name = name;
}
}
Bar = new MyBar()
Bar.setMyFoosName('Robert');
Gives it more of a global scope and so on, aslong as MyFoo is in the global scope.
Example here.
this referes to the scope of setMyFoosName. You should put this in a variable, and refer to that variable:
function MyFoo () {
this.name = 'myname';
}
function MyBar () {
var that = this;
this.myFoo = new MyFoo();
this.setMyFoosName = function( name ) {
that.myFoo.name = name;
}
}
Try to avoid exporting variables which should remain private:
function myFoo () {
this.name = 'myname';
}
function MyBar () {
/* myFoo is private */
var myFoo = new MyFoo();
this.setMyFoosName = function( name ) {
myFoo.name = name;
}
}
In this way, you cannot break your function with:
$.myBar = new MyBar();
$.myBar.myFoo = new EvilObject();
$.myBar.setMyFoosName();
Of course, this depends on your use, whether myFoo should be overridable or not.