I've been trying to learn Javascript. This is my code - I'm trying to implement a singleton - but for some reason, I get the error setMessage is not a function in the line firstInstance.setMessage("Message");. I have no idea what I'm doing wrong - any help would be greatly appreciated.
`
var mySingleton = (function () {
var instance;
var message;
function getInstance() {
if (!instance) instance = new Object();
return instance;
}
function setM (newMessage) {
message = newMessage;
return;
}
function getM() {
return message;
}
return {
createInstance:getInstance,
setMessage:setM,
getMessage:getM
}
})();
var firstInstance = mySingleton.createInstance();
var secondInstance = mySingleton.createInstance();
//set messages
firstInstance.setMessage("Message");
console.log(firstInstance.getMessage());
console.log(secondInstance.getMessage());
//change messages
secondInstance.setMessage("New");
console.log(firstInstance.getMessage());
console.log(secondInstance.getMessage());`
The setMessage and getMessage need to be on the instance you create, not in the object returned with the createInstance:
var mySingleton = (function() {
let instance;
let message;
function createInstance() {
if (!instance) instance = { setMessage, getMessage };
return instance;
}
function setMessage(newMessage) {
message = newMessage;
}
function getMessage() {
return message;
}
return { createInstance }
})();
var firstInstance = mySingleton.createInstance();
var secondInstance = mySingleton.createInstance();
firstInstance.setMessage("Message");
console.log(firstInstance.getMessage());
console.log(secondInstance.getMessage());
secondInstance.setMessage("New");
console.log(firstInstance.getMessage());
console.log(secondInstance.getMessage())
Related
I want to make a static array in a javascript class, for this I do:
var Manager = (function () {
function Manager() {
var ubications = new ArrayList();
this.ubicationsArray = function () {
return(ubication);
};
}
Manager.prototype.addUbication = function (ubication) {
Manager.ubicationsArray().add(ubication);
};
Manager.prototype.getUbication = function (index) {
return Manager.ubicationsArray().get(index);
};
Manager.prototype.sizeOfUbications = function () {
return Manager.ubicationsArray().size();
};
return Manager;
}());
Manager["__class"] = "Manager";
Where ubications is the static array and the function ubicationsArray is the public function to acces the array.
I try to use this code with:
var ubication = new Ubication(123,456);
var manager = new Manager();
manager.addUbication(ubication);
alert(manager.sizeOfUbications());
But I got this error:
Uncaught TypeError: Manager.ubicationsArray is not a function
How is the correct way to use static arrays in a javascript code?
Currently, JavaScript can only do privacy with respect to function scope.
function Manager () {
}
Manager.prototype = (function (){
var ubications = [];
return {
addUbication: function (u) {
ubications.push(u);
},
getUbication: function (index) {
return ubications[index];
},
sizeOfUbications: function () {
return ubications.length;
}
};
})();
Inside your constructor function, this.ubicationsArray assigns a property to the instance of the object, not the constructor itself.
Perhaps you want something like this:
function Manager() {
}
var ubications = new ArrayList();
Manager.ubicationsArray = function () {
return(ubication);
};
Note that this property isn't really "private". This would be more-private:
var Manager = (function () {
function Manager() {
}
var ubications = new ArrayList();
Manager.prototype.addUbication = function (ubication) {
ubications.add(ubication);
};
Manager.prototype.getUbication = function (index) {
return ubications.get(index);
};
Manager.prototype.sizeOfUbications = function () {
return ubications.size();
};
return Manager;
}());
Manager["__class"] = "Manager";
Suppose I have a function called log which simply prints the given string.
Can I refactor my code so both of these function could work?
log("needsChange").doSomethingWithTheStringBeforePrintingIt();
log("perfectStringToPrint");
You can do something similar with nested class logics:
var log = (function() {
//Class
var _log = (function() {
function _log(message) {
this.message = message;
}
_log.prototype.doSomethingWithTheStringBeforePrintingIt = function() {
this.message = this.message.split("").reverse().join("");
return this;
};
_log.prototype.capitalizeFirstWord = function() {
this.message = this.message[0].toUpperCase() + this.message.substr(1);
return this;
};
_log.prototype.print = function() {
return this.message;
};
return _log;
}());
//Instancer function
return function log(message) {
//Return instance of class
return new _log(message);
};
})();
//Test
console.log(log("needsChange")
.doSomethingWithTheStringBeforePrintingIt()
.capitalizeFirstWord()
.print(), log("perfectStringToPrint")
.print());
If you are comfortable with promises, then you can do something like this:
var logger = (function() {
//Class
var _log = (function() {
function _log(message) {
var _this = this;
this.message = message;
this.promise = null;
this.promises = [];
this.promise = Promise.all(this.promises).then(function(values) {
console.log(_this.message); // [3, 1337, "foo"]
});
}
_log.prototype.reverse = function() {
var self = this;
this.promises.push(new Promise(function(resolve, reject) {
setTimeout(resolve, 0, (function() {
self.message = self.message.split("").reverse().join("");
})());
}));
return this;
};
_log.prototype.capitalizeFirst = function() {
var self = this;
this.promises.push(new Promise(function(resolve, reject) {
setTimeout(resolve, 0, (function() {
self.message = self.message[0].toUpperCase() + self.message.substr(1);
})());
}));
return this;
};
return _log;
}());
//Instancer function
return function log(message) {
//Return instance of class
return new _log(message);
};
})();
//Test
logger("needsChange").reverse().capitalizeFirst().reverse(); //Capitalizes last letter
logger("perfectStringToPrint");
This removes the need for a .print call.
I have made a library to solve this issue
https://github.com/omidh28/clarifyjs
I need to use logic like visitor pattern and I've created new
sample which failed in visitor.visit(self); and I got error undefined is not a function,
any idea what am I missing?
var Entity = function (file,name) {
var self = this;
var name;
var type;
var log = {};
this.setName = function (name) {
this.name = name;
};
this.accept = function (visitor) {
visitor.visit(self);
};
this.getName = function () {
return name;
};
this.getType = function () {
return type;
};
this.getLog = function () {
return log;
};
};
//Start using visitor
var verifyFile = function () {
this.visit = function (file) {
alert("test");
};
};
function test(){
var file = new Entity();
file.accept(verifyFile);
};
You are injecting a function that defines a function, but your code is looking for an object that contains a function - see below
var Entity = function(file, name) {
var self = this;
var name;
var type;
var log = {};
this.setName = function(name) {
this.name = name;
};
this.accept = function(visitor) {
visitor.visit(self);
};
this.getName = function() {
return name;
};
this.getType = function() {
return type;
};
this.getLog = function() {
return log;
};
};
//Start using visitor
var verifyFile = {
visit : function(file) {
alert("test");
}
};
function test() {
var file = new Entity();
file.accept(verifyFile);
};
test()
Trying to implement singleton pattern in javascript following some tutorials. Just wondering if there is any other way to implement the same ?
var singleton = (function(){
var getInstance; //private variable
var createWidget = function(){
var todayDate = new Date(); //private
var addCSS = function(){
console.log('THis is my css function');
};
var getDropDownData = function(){
console.log('This is my getDropDownData function');
};
return {
getDropDownData : getDropDownData,
addCSS: addCSS
};
};
return {
getInstance: function(){
if(!getInstance) {
getInstance = createWidget();
}
return getInstance;
}
};
})();
var obj = singleton.getInstance();
Implementing it by running anonymous function at onLoad and assiging it to some variable. Can we implement it without running this function at onLoad ?
You could always write a function to abstract away the boilerplate for writing singletons. For example this is what I would do:
function singleton(prototype) {
var instance = null;
return {
getInstance: function () {
if (instance === null) {
var Instance = prototype.init || function () {};
Instance.prototype = prototype;
instance = new Instance;
} return instance;
}
};
}
Then you can use this function to create singletons as follows:
var Widget = singleton({
init: function () {
var todayDate = new Date; // private
},
addCSS: function () {
console.log("This is my addCSS function.");
},
getDropDownData: function () {
console.log("This is my getDropDownData function.");
}
});
After that you use the singleton as you normally would:
var widget = Widget.getInstance();
Hope that helps.
i'm practicing with Javascript Inheritance, my first try is following code:
var base_class = function()
{
var _data = null;
function _get() {
return _data;
}
this.get = function() {
return _get();
}
this.init = function(data) {
_data = data;
}
}
var new_class = function() {
base_class.call(this);
var _data = 'test';
function _getData() {
return this.get();
}
this.getDataOther = function() {
return _getData();
}
this.getData = function() {
return this.get();
}
this.init(_data);
}
new_class.prototype = base_class.prototype;
var instance = new new_class();
alert(instance.getData());
alert(instance.getDataOther());
to that point i am really happy with my solution, but there is one problem
that i dont get resolved.
the "getDataOther" method don`t return the stored data from the base class,
because i cannot access the public "get" class from the protected "_getData" method in the new_class.
How can i get that running ?
Thanks in advance.
Ps.: Please excuse my poor English
If you comment out the this.init function (which overwrites the base_class _data field) and make the new_class's getData function just return _data, you should be able to get distinct variables.
var base_class = function()
{
var _data = null;
function _get() {
return _data;
}
this.get = function() {
return _get();
}
this.init = function(data) {
_data = data;
}
}
var new_class = function() {
var self = this; //Some browsers require a separate this reference for
//internal functions.
//http://book.mixu.net/ch4.html
base_class.call(this);
var _data = 'test';
function _getData() {
return self.get();
}
this.getDataOther = function() {
return _getData();
}
this.getData = function() {
return _data; //Changed this line to just return data
//Before, it did the same thing as _getData()
}
//this.init(_data); //Commented out this function (it was changing the base_class' data)
}
new_class.prototype = base_class.prototype;
var instance = new new_class();
alert(instance.getData());
alert(instance.getDataOther());
Your english is fine by the way :)