Develop Reference

Javascript scope issues when binding

I know there are sooo many similar questions on stack regarding this issue, but for the life of me I cannot understand what the problem is in my code.
Trying to level up in javascript so any advise would be helpful. I have created an object to manage slider functions.
var gMapSlider = {
mapSlideShow: false,
// why doesnt current place update when passed in
newMarker: null,
oldMarker: null,
mapSlideIn: function() {
this.contentSlide
$('#placeDetails').animate({right: '0'});
this.mapSlideShow = true;
},
mapSlideOut: function(func) {
if (typeof(func) != "function") func = function() {};
$('#placeDetails').animate({right: '-320px'}, null, null, func());
this.mapSlideShow = false;
},
mapSlideToggle: function() {
(this.mapSlideShow) ? this.mapSlideOut() : this.mapSlideIn();
},
contentSlide: function() {
if (this.newMarker) $('h1', '#placeDetails').text(this.newMarker.title);
},
mapSlide: function(marker) {
this.newMarker = marker;
if (this.oldMarker === this.newMarker) { //same marker showing
this.mapSlideToggle();
}
else if (this.oldMarker !== this.newMarker && !this.mapSlideShow) { //diff marker showing
this.contentSlide(marker);
this.mapSlideIn();
}
else if (this.oldMarker !== this.newMarker && this.mapSlideShow) {
var self = this;
console.log(self) //returns this object
this.mapSlideOut(function() {
console.log(self); // returns this object
self.contentSlide(this.newMarker);
self.mapSlideIn;
}).bind(self); // cannot read property 'bind' of undefined
}
this.oldMarker = this.newMarker;
}
}
A couple of questions
1) The problem is with my gMapSlider.mapSlide function. If I call the mapSlide function and the last else if statement applies I get a cannot read property of bind error. I have Google'd but found nothing of any real relevance. Can anyone help with what I am doing wrong here.
2) Is this the best way of managing functions within a namespace. Most code samples I see use functions in the global namespace so wanted a bit of clarification if it is advised to create objects like this in Javascript?
EDIT #torazaburo Thanks, feel like a proper Newbie, that was the issue. Put it as an answer and I will put as solved. Any advice on code architecture?

this.mapSlideOut(function() {
console.log(self); // returns this object
self.contentSlide(this.newMarker);
this.mapSlideIn;
}).bind(self);
bind() should be called on a function object but you'r calling it on the result of a function call
use this:
this.mapSlideOut.bind(self,function() {
console.log(this); // returns this object
this.contentSlide(this.newMarker);
this.mapSlideIn;
});
also the above call will return you a reference to the function with this bound to self

Angular services with default values for non-existing attributes

Working on an Ionic application that performs both in Android and Windows.
There are services, such as Ionic's $ionicLoading, which we override functionality in order to work properly in windows:
angular.factory('$ionicLoading', function(){
return {
show: function (){...} // custom implementation
hide: function (){...} // custom implementation
}
});
But there are other services which we have to override only to not break the app.
In this cases it would be really useful to provide a service that won't do anything. For example:
angular.factory('$ionicExampleService', function(){
return {
*foo*: angular.noop // for operations
*bar*: promise // returns promise
}
});
Note: I know that a better way of doing this would be with a service that chooses between Ionic's implementation or a made one, but this is just for the sake of learning.
The ideal would be going even further, it would be magnificent to be able to return something even more bulletproof. Something like a generic flexible services:
angular.factory('$ionicPopup', function(){
return /*magic*/;
});
$ionicPopup.show({...}) // show was not defined
.then(foo); // won't break and will execute foo()
It is possible?

From what I understood you need to override implementation of existing services. You can do that with an angular service decorator.
A service decorator intercepts the creation of a service, allowing it to override or modify the behaviour of the service. The object returned by the decorator may be the original service, or a new service object which replaces or wraps and delegates to the original service.
For more information you can check angular documentation. One simple example would be:
app.factory('someService', function () {
return {
method1: function () { return '1'; }
method2: function () { return '2'; }
};
});
app.decorator('someService', function ($delegate) {
// NOTE: $delegate is the original service
// override method2
$delegate.method2 = function () { return '^2'; };
// add new method
$delegate.method3 = function () { return '3'; };
return $delegate;
});
// usage
app.controller('SomeController', function(someService) {
console.log(someService.method1());
console.log(someService.method2());
console.log(someService.method3());
});
EDIT: Question - How to override every method in the service?
var dummyMethod = angular.noop;
for(var prop in $delegate) {
if (angular.isFunction($delegate[prop])) {
$delegate[prop] = dummyMethod;
}
}
I hope that this helps you.

Using an evaluation for each assignment based on an object property, similar to this:
myVar = myObj.myPropVar === undefined ? "default replacement" : myObj.myPropVar;
Basically you're using a check for if the property has been defined, substituting a default value if it hasn't, and assigning it if it has.
Alternatively, you can use a modified version of the global function in Sunny's linkback to define defaults for all those properties you might assume to be undefined at specific points in your code.
function getProperty(o, prop) {
if (o[prop] !== undefined) return o[prop];
else if(prop == "foo") return "default value for foo";
else if(prop == "bar") return "default value for bar";
/* etc */
else return "default for missing prop";
}
Hope that helps,
C§

use var a = {}; to declare new variable.

How to reference a custom jQuery validator method in an $.ajax() success callback?

My apologies for the one millionth iteration of this type of question. I've already seen a number of other posts talking about this, and I still can't wrap my head around being able to invoke a function after the callback is successful and returns. I must have read this post over half a dozen times:
How do I return the response from an asynchronous call?
The Code
Anyway .., my question I hope anyone could shed some light on. I have a custom jQuery validator method that checks if a username is available.
jQuery.validator.addMethod("usernameAvailability",
function(value, element) {
console.log('starting usernameAvailability');
if(this.optional(element) === true){return true;}
else{
console.log('ending usernameAvailability, about to return get_availability');
return availabilityCheck.get_availability('username');
}
}, "Username already in use." );
The custom jQuery validator method calls get_availability(element) in namespace availabilityCheck.
var availabilityCheck = (function() {
var usernameIsAvailable, emailIsAvailable, Callback, AJAX_Availability_Check, change_Availability;
usernameIsAvailable = null;
emailIsAvailable = null;
AJAX_Availability_Check = function(callback, element){
console.log('starting AJAX_Availability_Check');
if(element==="username"){
selection = {username:$('#id_username').val()};
}
else{
selection = {email:$('#id_email').val()};
}
$.ajax({
url: '/register/',
type: 'get',
data: selection,
dataType:'text',
async: true
}).done(Callback(element));
};
change_Availability = function(element, bool) {
if(element === 'username'){
usernameIsAvailable = bool;
}
else{
emailIsAvailable = bool;
}
};
Callback = function(element) {
return function(result, textStatus){
bool = result === "True" ? true: false;
change_Availability(element, bool);
return usernameIsAvailable;
};
};
return{
get_availability: function(element){
AJAX_Availability_Check(Callback, element);
return element === 'username' ? usernameIsAvailable : emailIsAvailable;
}
}
})();
The Problem and My Question
My problem The input correctly validates whether the username is already in use, but the user needs to trigger validation twice since get_availability returns before the Callback can change usernameIsAvailable to the proper boolean.
My Question How do I restructure my code so my custom jQuery validate method is invoked by the callback? Or how do I ensure that it won't validate until the Callback returns?

The problem is your structure... I don't know where you got that from but throw it away and burn it, then forget you ever saw it.
You can simplify your code to look like this:
var availabilityCheck = function() {
var usernameIsAvailable = null, emailIsAvailable = null,
AJAXAvailabilityCheck, changeAvailability;
AJAXAvailabilityCheck = function(element){
console.log('starting AJAX_Availability_Check');
if(element==="username"){
selection = {username:$('#id_username').val()};
}
else{
selection = {email:$('#id_email').val()};
}
$.ajax({
url: '/register/',
type: 'get',
data: selection,
dataType:'text',
async: true
}).done(changeAvailability(element));
};
changeAvailability = function(element, theBool) {
if(element === 'username'){
usernameIsAvailable = theBool;
}
else{
emailIsAvailable = theBool;
}
};
this.getAvailability = function(element) {
AJAXAvailabilityCheck(element);
return element === 'username' ? usernameIsAvailable : emailIsAvailable;
}
};
So your callback is now actually something useful instead of just another useless layer.
However as I point out below, your result wasn't ever actually defined as far as I could tell so your going to have to figure out what theBool should be.
Some things of note:
Callback = function(element) {
return function(result, textStatus){
bool = result === "True" ? true: false;
change_Availability(element, bool);
return usernameIsAvailable;
};
};
You return an anonymous function for no particular reason, and your result variable isn't defined... at least with the code as you have it, so with what you have it's always resolving to false. Also if your just checking for truthyness then you don't need a tuple you can just do result === "True" which will evaluate to true or false, no need for the extra ? true : false.
Also, don't use words like bool for variable names. Bool is a type of variable and is a reserved word. Javascript lets you use it cause... Javascript will let you do just about anything, but its bad practice.
Finally you mixed like 10 different types of casing. Now casing is a personal preference (I personally prefer underscores to camelCase, which is the javascript convention), but no matter what case you use. USE ONLY ONE CASE!
Now I believe your real issue here is that you don't understand what a self-invoking function is for.
You use this syntax: var availabilityCheck = (function(){})(); which creates a self-invoking function; which means that it's going to fire without being called! Which means all this does is call your ajax and cause an extraneous server hit when your user hasn't even entered any data yet.
I believe that you did it so you could use this syntax availabilityCheck.getAvailability() in your invoking function, but the better way to do that is to do what I did above and make getAvailability a property of availabilityCheck by using the this keyword. Then you can use the same syntax without running your whole function twice.
You should almost NEVER (there are always exceptions of course) put an ajax call in a self invoking function. If the call doesn't depend on user input, then you should of just loaded the data when your page was requested the first time.

Javascript running code once

I only want my JavaScript to run once, but I cannot control how many times the javascript file is executed. Basically I'm writing a tiny JS snippet into a CMS, and the CMS is actually calling it 5-10 times. So solutions like this:
function never_called_again(args) {
// do some stuff
never_called_again = function (new_args) {
// do nothing
}
}
never_called_again();
Don't seem to work because as soon as my snippet is run again from the top the function is re-declared, and 'do some stuff' is re-evaluated. Perhaps I'm just not doing it properly, I'm not great with JS. I'm considering using something like try-catch on a global variable, something like
if (code_happened == undefined) {
\\ run code
code_happened = true;
}
EDIT: There is a consistent state e.g. if I set a variable I can see when my snippet is run again. But having to declare it before I access it, I don't know how to say 'does this variable exist yet'

Try this:
var doneTheStuff;
function whatever() {
if (!doneTheStuff) {
doneTheStuff = true;
// do the stuff
}
}
Redundant variable declarations don't affect the value of the variable. Once one of the functions has set the variable to true, the others won't do anything.

if (typeof code_happened === 'undefined') {
window.code_happened = true;
// Your code here.
}
The typeof check gets you around the fact that the global hasn't been declared. You could also just do if (!window.code_happened) since property access isn't banned for undefined properties.

Use a closure, and set a flag. If the flag is true, just return:
if ( ! window.never_called_again ) {
window.never_called_again = (function () {
var ran = false;
return function (args) {
if ( ran ) return;
ran = true;
// Do stuff
};
}());
}
Here's the fiddle: http://jsfiddle.net/U2NCs/

With jQuery, the function .one() may be useful : http://api.jquery.com/one/
W3School exemple here : http://www.w3schools.com/jquery/event_one.asp

In this way, the code is executed only once.
if(typeof onceRun == "undefined") window.onceRun=(
()=>{
//your codes...
console.log("runing...")
return true
}).call()

jQuery/Javascript: How can I evaluate the validity of function arguments efficiently with a range of valid types?

I've got a rather large plugin that I am currently writing in jQuery which is using a lot of internal functions that can accept varying arguments depending on the function.
I caught myself constantly writing the following in every function to stop the code from running if an argument hasn't been supplied or isn't valid:
add : function(args) {
if (args===undefined) return;
// function code;
},...
I was hoping that in a DRY type of sense it would be a good idea to write a little internal helper function that would do this for me.
Is this actually a good idea and most importantly what is the best/secure way to check for a varied range of acceptable arguments?
There are a lot of functions with multiple arguments in this plugin, for example:
load : function( filename , path , excludeFromRandom , callback ) {}
where filename is a string,
path is a string,
excludeFromRandom is a boolean and
callback can be a function or a string.
What is a good way to check for the existence and validity of these types of arguments without rewriting the same code over and over?
Any suggestions and ideas would be great.
Thanks for reading.

It depends to what extent you want to do this. In idea would be to create a validation function which takes a argument -> rule mapping. E.g.:
function foo(somestring, somenumber) {
var rules = {
'somestring': Validator.rules.isString,
'somenumber': Validator.rules.inRange(5,10);
};
}
Validator would contain the basic logic and some helper functions (rules):
var Validator = {
valid: function(args, rules) {
for(var name in rules) {
if(!rules[name](args[name])) {
return false;
}
}
return true;
},
rules: {
isString: function(arg) {
return (typeof arg === 'string');
},
inRange: function(x,y) {
return function(arg) {
return !isNaN(+arg) && x <= arg && arg <= y;
}
}
}
}
This is just a sketch, it certainly can be extended (like accepting multiple rules per argument), but it should give you some idea.
That said, you don't have to check every argument. Provide decent documentation. If people use your plugin in a wrong way, i.e. passing wrong argument types, then your code will throw an error anyway.
Update:
If want to do this very often, then a good idea is to write a wrapper function and you just pass the function and the rules to it:
function ensure(func, rules, context) {
context = context || this;
return function() {
if(Validator.valid(arguments, rules)) {
return func.apply(context, arguments);
}
return null; // or throw error, whatever you want
}
}
Then you can define your function normally as:
var foo = function(somestring, somenumber) {
// ...
};
and just add validation to it:
var rules = {...};
foo = ensure(foo, rules);
You could even consider to make ensure accept a callback which gets called on error or success of the function, instead of returning a value. There are a lot of possibilities.