I spent the better part of the day reading about the module pattern and its 'this' scope. Eventually I found a work-around for my problem, although with a feeling there's a better way of doing things.
The actual code is >200 lines, but I've boiled it down to the following:
objA has a method (publicA) that objB wants invoke by callback. The detail that complicates things is that publicA needs help from publicA_helper to do its job. (http://jsfiddle.net/qwNb6/2/)
var objA = function () {
var privateA = "found";
return {
publicA: function () {
console.log("privateA is " + this.publicA_helper());
},
publicA_helper: function () {
return privateA;
}
};
}();
var objB = function () {
return {
callback: function (callback) {
callback();
}
}
}();
objA.publicA(); // privateA is found
objB.callback(objA.publicA); // TypeError: Object [object global]
Fair enough – I've grasped that the caller's context tends to influence the value of 'this'. So I add measures to retain 'this' inside objA, of which none seems to work. I've tried the
var objA = (){}.call({}) thingy, setting var self = this; (calling self.publicA_helper() accordingly). No luck.
Eventually, I added a private variable var self;, along with a public method:
init: function() {self = this;},
...and by making sure I call objA.init(); before passing objA.publicA to objB.callback, things actually work.
I cannot stress the immensity of the feeling that there's a better way of doing this. What am I missing?
The generalized solution is extremely simple.
Write all the module's methods as private, then expose those that need to be public.
I write all my modules this way :
var objA = function () {
var privateA = "found";
var A = function () {
console.log("privateA is " + A_helper());
},
var A_helper = function () {
return privateA;
}
return {
publicA: A
//A_helper need not be exposed
};
}();
Thus, all methods are in the same scope, each one having direct access to all other methods in the same module, and the ambiguous this prefix is avoided.
objB.callback(objA.publicA); will now work as expected.
See fiddle
I've tried the var objA = (){}.call({}) thingy,
How? You want to use call on the callback that you want to invoke with a custom this, not on your module closure. It should be
var objB = {
callback: function (callback, context) {
callback.call(context);
}
};
objB.callback(objA.publicA, objA);
I've tried setting var self = this;
The self variable is supposed to be in a closure and point to the object on the methods are stored. That is only this when your module IEFE would be invoked on your module - it's not. Or if it was a constructor - it's not. You could change that with call as above:
var objA = function () {
var privateA = "found",
self = this;
this.publicA = function () {
console.log("privateA is " + self.publicA_helper());
};
this.publicA_helper = function () {
return privateA;
};
return this;
}.call({});
But that's ugly. In your case, the self variable simply needs to point to the object literal which you're returning as your module:
var objA = function () {
var privateA = "found",
self;
return self = {
publicA: function () {
console.log("privateA is " + self.publicA_helper());
},
publicA_helper: function () {
return privateA;
}
};
}();
Btw, since you're creating a singleton you don't need an explicit self, you could just reference the variable that contains your module (as long as that doesn't change):
var objA = function () {
var privateA = "found";
return {
publicA: function () {
console.log("privateA is " + objA.publicA_helper());
},
publicA_helper: function () {
return privateA;
}
};
}();
Another method would be to simply make all functions private and then expose some of them - by referencing them local-scoped you will have no troubles.
var objA = function () {
var privateA = "found";
function publicA() {
console.log("privateA is " + helper());
}
function helper() {
return privateA;
}
return self = {
publicA: publicA,
publicA_helper: helper // remove that line if you don't need to expose it
};
}();
The reason is that the context is getting changed when you are invoking the callback. Not a generalized solution, but shows that the code works by specifying the context while invoking callback.
var objA = function () {
var privateA = "found";
return {
publicA: function () {
console.log("privateA is " + this.publicA_helper());
},
publicA_helper: function () {
return privateA;
}
};
}();
var objB = function () {
return {
callback: function (callback) {
callback.call(objA);
}
}
}();
objA.publicA(); // privateA is found
objB.callback(objA.publicA); // privateA is found
Related
I have the below code:
filtersManager = (function ($) {
var that = this;
function configure() {
// some work
return that;
};
function process() {
// some work
return that;
}
return {
// public functions
configure: configure,
process: process
};
}(jQuery));
but when it's called using the below it fails:
filtersManager.configure().process();
Error: Object doesn't support property or method 'process'
whereas the below works:
filtersManager.configure();
filtersManager.process();
You are returning the wrong thing (this in a plain function invocation is the global object). You want to return the object that you originally created, which I will call the interface.
filtersManager = (function ($) {
var interface = {
// public functions
configure: configure,
process: process
};
function configure() {
// some work
return interface;
};
function process() {
// some work
return interface;
}
return interface;
}(jQuery));
If you're wondering why I can reference the functions defined below, it's due to hoisting.
Immediate function is executed in global object (window) context. Try something similar to this:
filtersManager = (function ($) {
var that = {};
that.configure = function() {
// some work
return that;
};
that.process = function() {
// some work
return that;
}
return that;
}(jQuery));
UPD. Based on comments
Constructor pattern seems to fit your need better:
var FiltersManager = (function($) {
function FiltersManager() {}
FiltersManager.prototype = {
configure: function() {
console.log('configure');
return this;
},
process: function() {
console.log('process');
return this;
}
}
return FiltersManager;
}(jQuery));
new FiltersManager().configure().process();
As to continue what others have said , I think you confused with the function constructor syntax which would work , similar to what you've said ;
var G=function g()
{
this.configure =function (){return this;}
this.process =function (){return this;}
};
var _= new G();
console.log(_.configure().process())
If you wanted to re-use the functions on other objects too, you could do it like this
filtersManager = function ($) {
function configure() {
// some work
return this;
};
function process() {
// some work
return this;
}
return {
// public functions
configure: configure,
process: process
};
}(jQuery);
(OTOH, if you wanted to create aliases to them, you would then have to bind them to the object)
Or if configure and process are quite short, simple functions :
filtersManager = (function ($) {
return {
// public functions
configure: function () {
// some work
return this;
},
process: function () {
// some work
return this;
}
};
}(jQuery));
In JavaScript I am looking for a way to use bind() on an anonymous and async function.
Example:
exports.foo = function () {};
exports.foo.prototype = {
load : function(id) {
var query = new Parse.Query("SomeObject");
query.get(id).then(function(object) {
this.object = object; // this is the wrong this
});
}
};
I got this working by making the functions non-anonymous, but I think it makes my code look ugly. Especially after having 4 different anonymous functions in a row.
exports.foo = function () {};
exports.foo.prototype = {
load : function(id) {
function _load(object) {
this.object = object;
}
var _loadThis = _load.bind(this);
var query = new Parse.Query("SomeObject");
query.get(id).then(_loadThis);
}
};
Is there a better way?
Well it's not necessarily "better", but you can call .bind() directly after the closing brace of your function instantiation expression:
query.get(id).then(function(object) {
this.object = object; // this is the wrong this
}.bind(this));
A function instantiation expression gives you a function object reference, so putting a . after it and calling bind makes sense. What gets passed to the .then function, therefore, is the return value from the call to .bind.
This syntax is not correct:
exports.foo.prototype = {
load = function(id) {
var query = new Parse.Query("SomeObject");
query.get(id).then(function(object) {
this.object = object; // this is the wrong this
});
}
};
The prototype is an object who's properties are defined as load: function() {}, not load = function() {}.
It should be:
exports.foo.prototype = {
load: function(id) {
var query = new Parse.Query("SomeObject");
query.get(id).then(function(object) {
this.object = object; // this is the wrong this
});
}
};
A simple way to do it is to declare a variable to the correct 'this' and use closuers to keep a reference to it.
exports.foo = function () {};
exports.foo.prototype = {
load : function(id) {
var self = this;
var query = new Parse.Query("SomeObject");
query.get(id).then(function(object) {
self.object = object; // this is the wrong this
});
}
};
I have the following code
var PROMO = PROMO || {};
PROMO.Base = (function () {
var _self = this;
var Init = function () {
WireEvents();
};
var WireEvents = function () {
//wire up events
};
} ());
In the same file I have the code to call the above function
I am trying to get to an end point where I can use the following code
$(document).ready(function () {
PROMO.Base.Init();
});
this gives the error
Cannot call method 'Init' of undefined
Now I know there are many ways to write javascript, but in this case I want to be able to call my functions, or least the Init method in the way shown above.
var PROMO = PROMO || {};
PROMO.Base = (function () {
var _self = this;
var Init = function () {
WireEvents();
};
var WireEvents = function () {
//wire up events
};
var reveal = {
Init: Init
};
return reveal;
} ());
You need to return the public facing functions. See updated code.
Working fiddle with both patterns, using IIFE and direct attribution.
Using var makes the definition private and your function is returning nothing. Use this:
PROMO.Base = {
Init: function() {
},
WireEvents: function() {
};
};
You are wrapping the definition with an IIFE(Immediately Executed Function Expression). So your PROMO.Base object will be assigned the value of that (function(){//blabla})(); returns. But your function doesn't have a return statement. By default it will return undefined.
Which is way your PROMO.Base will be undefined and you get this:
Cannot call method 'Init' of undefined
If you really want that IIFE:
var PROMO = PROMO || {};
// NEVER use _self = this inside static functions, it's very dangerous.
// Can also be very misleading, since the this object doesn't point to the same reference.
// It can be easily changed with Function.prototype.call and Function.prototype.apply
PROMO.Base = (function () {
_PROMO = {
Init : function () {
document.body.innerHTML += "itworks";
},
WireEvents : function () {
//wire up events
}
}
return _PROMO;
} ());
PROMO.Base.Init();
Update
The better and easier pattern is to simply assign the functions to PROMO.Base. Dully note you should not capitalize static functions, but only constructors. So if something is not meant to be instantiated, don't call it Init, it should be init. That is the convention.
var PROMO = {};
PROMO.Base = {};
PROMO.Base.init = function() {
console.log("this works");
};
PROMO.Base.wireEvents = function() {
console.log("this is a static function too");
};
You can attach it to the window object like ...
window.PROMO = (function($, _){
// this will access PROMO.Base
PROMO.Base = {
// inner functions here
Init:{}
};
})(jQuery, _);
Then load it as you do.
Or if you depend from jQuery
(function($){
var PROMO = {
// inner functions
Init: function(){},
WireEvents: function(){}
};
$.PROMO = PROMO;
})(jQuery);
On DOM ready
jQuery(function ($) {
var promo = $.PROMO || undefined;
promo.Base.Init();
});
I am writing some JavaScript code. I am a little confused about this keyword. How do I access logger variable in the dataReceivedHandler function?
MyClass: {
logger: null,
init: function() {
logger = LogFactory.getLogger();
},
loadData: function() {
var dataReceivedHandler = function() {
// how to access the logger variable here?
}
// more stuff
}
};
You can do something like this inside the loadData function to access your object...
MyClass: {
logger: null,
init: function() {
this.logger = LogFactory.getLogger();
},
loadData: function() {
var self = this;
var dataReceivedHandler = function() {
// how to access the logger variable here?
self.logger.log('something');
}
// more stuff
}
};
Assuming loadData is called like so:
MyClass.loadData();
then:
loadData: function() {
var self = this;
var dataReceivedHandler = function() {
self.logger ...
}
// more stuff
}
Because dataReceivedHandler is an anonymous function this will refer to the window object on the global scope. I think of two way you can bypass that.
a) Create a variable inside loadData to hold it's context then use it inside dataReceivedHandler as such:
loadData: function() {
var self = this;
var dataReceivedHandler = function() {
console.log(self.logger);
}
// more stuff
}
b) Change the context of your anonymous function using apply or call.
loadData: function() {
var dataReceivedHandler = function() {
console.log(this.logger);
}
// more stuff
dataReceivedHandler.call(this); // by passing this as the first argument we make sure the context of the excuted function is our current scope's this
}
I prefer option B due to performance and memory usage optimizations, but both would work just fine.
I have the following piece of code:
function initValidation()
{
// irrelevant code here
function validate(_block){
// code here
}
}
Is there any way I can call the validate() function outside the initValidation() function? I've tried calling validate() but I think it's only visible inside the parent function.
function initValidation()
{
// irrelevant code here
function validate(_block){
console.log( "test", _block );
}
initValidation.validate = validate;
}
initValidation();
initValidation.validate( "hello" );
//test hello
Hope that you are looking for something like this
function initValidation()
{
// irrelevant code here
this.validate = function(_block){
// code here
}
}
var fCall = new initValidation()
fCall.validate(param);
This will work.
Hope this addresses your problem.
You can call validate from within initValidation. Like this.
function initValidation()
{
// irrelevant code here
function validate(_block){
// code here
}
return validate(someVar);
}
validate is not visible to anything outside of initValidation because of its scope.
Edit: Here's my suggestion of a solution.
(function() {
function validate(_block){
// code here
}
function initValidation()
{
// irrelevant code here
return validate(someVar);
}
function otherFunctions() {
// ...
}
// initValidation = function
}());
// initValidation = undefined
All of your functions will be hidden to anything outside the function wrapper but can all see each other.
This invocation will return function statement, which is function validate.
So you can invoke directly after the first invocation.
function initValidation() {
// irrelevant code here
return function validate(_block) {
// code here
}
}
initValidation()();
I know this is an old post but if you wish to create a set of instances that you wish to work with that reuse the code you could do something like this:
"use strict";
// this is derived from several posts here on SO and ultimately John Resig
function makeClassStrict() {
var isInternal, instance;
var constructor = function(args) {
if (this instanceof constructor) {
if (typeof this.init == "function") {
this.init.apply(this, isInternal ? args : arguments);
}
} else {
isInternal = true;
instance = new constructor(arguments);
isInternal = false;
return instance;
}
};
return constructor;
}
var MyClass = makeClassStrict();// create "class"
MyClass.prototype.init = function(employeeName, isWorking) {
var defaultName = 'notbob';
this.name = employeeName ? employeeName : defaultName;
this.working = !!isWorking;
this.internalValidate = function() {
return {
"check": this.working,
"who": this.name
};
};
};
MyClass.prototype.getName = function() {
return this.name
};
MyClass.prototype.protoValidate = function() {
return {
"check": this.working,
"who": this.name
};
};
var instanceBob = MyClass("Bob", true);// create instance
var instanceFred = MyClass("Fred", false);// create instance
var mything = instanceFred.internalValidate();// call instance function
console.log(mything.check + ":" + mything.who);
var myBobthing = instanceBob.protoValidate();
console.log(myBobthing.check + ":" + myBobthing.who);
I know this thread's been here for quite some time but I thought I'd also leave my 0.02$ on how to call inner functions from outside their scope (might benefit somebody).
Note that in any place, a better design decision should be taken into consideration rather than some hackish workaround which will bite you back later.
How about using function expressions instead of function statements and making use of the global scope.
var innerFn;
function outerFn() {
innerFn = function(number) {
return number ** 2;
}
}
outerFn();
console.log(innerFn(5));
// if there's more complex code around and you could write this defensively
if (typeof innerFn !== 'undefined') {
console.log(`we are squaring the number 5 and the result is: ${innerFn(5)}`);
} else {
console.log('function is undefined');
}
Or, you can make use of closures:
function outer() {
// initialize some parameters, do a bunch of stuff
let x = 5, y = 10;
function inner() {
// keeps references alive to all arguments and parameters in all scopes it references
return `The arithmetic mean of the 2 numbers is: ${(x + y) / 2}`;
}
return inner;
}
innerFn = outer(); // get a reference to the inner function which you can call from outside
console.log(innerFn());
Create a variable outside the parent function, then in the parent function store your required function in the variable.
Var Store;
Function blah() {
Function needed() {
#
}
Store = needed;
}
As a minor variation of Esailija's answer, I did this:
function createTree(somearg) {
function validate(_block) {
console.log( "test", _block );
}
if (somearg==="validate") { return validate; } // for addNodes
// normal invocation code here
validate(somearg);
}
function addNodes() {
const validate = createTree("validate");
//...
validate( "hello" );
}
createTree("create");
addNodes();
//validate("illegal");
so validate() is now perfectly shared between createTree() and addNodes(), and perfectly invisible to the outside world.
Should work.
function initValudation() {
validate();
function validate() {
}
}
Function definition:
function initValidation() {
// code here
function validate(_block){
// code here
console.log(_block);
}
return validate;
}
Call it as below:
initValidation()("hello");
function initValidation()
{
function validate(_block){
console.log(_block)
// code here
}
// you have to call nested function
validate("Its Work")
}
// call initValidation function
initValidation()