I have an MVC 4 project that utilizes javascript bundling.
In my _Layout.cshtml page I have something like this:
#Scripts.Render("~/bundles/scripts/desktop/modernizr",
"~/bundles/scripts/desktop/jquery","~/bundles/scripts/desktop/jqueryui",
"~/bundles/scripts/desktop/jqueryvalidation", "~/bundles/scripts/custom")
There are others, but this is just an example. Within one of my scripts that's called in the custom script I need to reference a global variable that set within the ready function, as shown below:
<script type="text/javascript">
$(function () {
//alert('Page is ready!');
var warning = 10;
var timeout = 20; }); </script>
Problem is, I always seem to get an error within the method that requires the warning and timeout variables. Am I missing something obvious (not to me, though!) on how I should create these variables? Should I var them outside the $Ready, because the js is loading before the page is technically ready?
Where should the global variable go, if everything is already in a render bundle and there are no script blocks?
Thanks!
The warning and timeout variables aren't global. They've only been defined within the function that you provide to the $ function.
I'd generally recommend avoiding global variables where possible, but if you really want to create global variables just use this:
<script type="text/javascript">
var warning = 10;
var timeout = 20;
</script>
Or this:
<script type="text/javascript">
$(function () {
window.warning = 10;
window.timeout = 20;
});
</script>
Thanks for the response.
I don't think adding the variables in the Ready page will work. The functions that require these variables are loaded before the page is 'ready' (per my understanding how this all works), so there are situations on a new page load where the variable will be required but unreferenced.
This is how I'm currently handling it:
I created a new .js file, with the following:
var warning;
var timeout;
Then I created a bundle reference to the file and put it into my #Script.Render stmt in the correct order for scope. Now, I have my global variables, and it's cleanly implemented into my view code. Now, I know that I should be passing around variables vs. having them global, but in this case I don't see a major issue.
Related
One of the views in my Rails 4 app loads a simple javascript to create an instance of the Ace editor once the page loads...
$(function() {
var editor = ace.edit("editor");
}):
In that view, I have a simple ajax button...
<%= button_to "Set Content", {controller: :pages, action: 'set_content'}, remote: true %>
that requests some unobtrusive javascript...
editor.setValue("New content has been set");
but this doesn't work. I'm guessing this doesnt work because editor isn't defined. Since ajax calls fail silently and I don't know how to debug unobtrusive javascript code using the same Chrome tools that I use debug normal javascript code, I can't verify that's the actual problem, but that's my best guess.
I was under the impression that if I write var editor, then is declared as a global variable that my unobtrusive javascript should be able to access.
My questions are...
How can I access global variables inside of my unobtrusive javascript code?
Since global variables are considered evil, is there a better way to access the editor variable from my unobtrusive javascript?
Thanks in advance for your wisdom!
when you use the var keyword inside a function, the scope of that variable is local to the function, so you are incorrect in your assumption about global scope. To make the variable global, declare it outside of your function:
var editor;
$(function(){
editor = ace.edit('editor');
});
alternatively you could simply reference the window object (which is the 'global' object in browsers
$(function(){
window.editor = ace.edit('editor');
});
With regards to avoiding global variables, it is reasonable to use a single global variable (often called 'app', or 'myCompany' or such to provide a namespace that is globally accessible.
var app = {};
$(function(){
app.editor = ace.edit('editor');
});
This at least limits the scope of your new variables so you don't mistakenly overwrite global variables. However the real answer to avoiding global variables lies in the overall architecture of your app, which can't really be addressed without seeing more code. Generally speaking if ALL of the code you write is inside your jquery ready function, then you don't need global variables. Frameworks such as angular, ember, and backbone provide a much better structure for this type of thing than the ad-hoc code common with simple uses of jquery.
$(function() {
var editor = ace.edit("editor");
});
creates a local variable editor within the context of it's callback function. To access it elsewhere, you'll need to make it global window.editor = ace.edit("editor"), or add it to a namespace with something like
window.App = {};
App.editor = ace.edit("editor");
Iam a new guy in JS and iam doing a mobile project in phonegap, i want to know how to keep a variable in overall page scope, not global variable since it will eat lot of memory which is not acceptable for a mobile developer, i have two or more JS tags in a page as shown,
<script type="text/javascript">
// script one here
</script>
<html> //html block here </html>
<script type="text/javascript">
// script two here
</script>
so i request your valuable suggestion & help. Thanks!
"Overall Page scope" is global scope.
JavaScript scoping (generally, except for specific esoteric scopes*) works in two ways:
Global scope
Closure scope (the scope created by a function)
Since you can't share a function over script tags, a global is your only choice.
Consider passing messages to share data instead of a global.
Here is how something like this could be done with message passing:
Script 0:
window.pubsub = (function(){
var subscribers = [];
return {
subscribe:function(user){
subscribers.push(user);
},
publish:function(message,data){
subscribers.forEach(function(elem){
elem.onMessage(data);
});
}
};
})();
Script 1:
(function(pubsub){
var someObject = {}; // to share state
//code here
pubsub.subscribe(someObject);
someObject.onMessage = function(){
//whatever you do when you get a message
};
})(window.pubsub);
Script 2 would be identical, only it would handle messages differently.
This way, you have one global variable (if that's too much, you can even delete window's reference to it after subscribing script 2, which would mean no globals at all)
*technically try/catch and with also introduce scope, but they're very rare and should not be used like this
I'm trying to use tripleflap.js in my app. My view is calling the function:
<script type='text/javascript' charset='utf-8'>
TwitterBird();
</script>
So, in application.js:
function TwitterBird() {
var twitterAccount = 'ulmicru';
var showTweet = false;
var birdSprite='http://127.0.0.1/birdsprite.png';
tripleflapInit();
}
Then I'm trying to run it, and Javascript debugger says me:
Uncaught ReferenceError: birdSprite is not defined
In precompiled application.js in /public/assets/ I'm watching this:
function TwitterBird()
{var e="ulmicru",t=!1,n="http://127.0.0.1/birdsprite.png";tripleflapInit()}
It seems Rails precompiler had renamed variables, and tripleflap.js cannot find them.
Is it possible to disable variable renaming in assets?
Try to move the variable definitions outside of the function, or just remove the var from in front of them, like this:
function TwitterBird() {
twitterAccount = 'ulmicru';
showTweet = false;
birdSprite='http://127.0.0.1/birdsprite.png';
tripleflapInit();
}
I googled the tripleflapInit script and took a look at it. Basically it defines a bunch of configuration variables directly on the window and expects you to overwrite them; a pretty kludgy script all in all, but that's beside the point.
Because you're defining birdSprite inside a function with var, you're actually defining a new variable local to that function. Even if it was not renamed by the minifier, the window-defined tripleflapInit would still not use it, but rather look to the variable defined on the window.
I'm not sure why you're getting the error that birdSprite is not defined, but it's possible that the compiler became confused and removed it, thinking it was unused.
I am currently coding in this way:
<script type="text/javascript">
var linkObj;
Is this a safe way to store data? My concern is what if a jQuery or other plug-in was to also use the variable linkObj. Also if I declare my variable like this then can it also be seen by other functions in scripts located in other js files that I include?
$(document).ready(function(){
var linkObj;
});
as long as you use the var keyword, any variable defined in that scope won't be accessible by other plugins.
I you declare a variable this way it will be accessible to all scripts running on the page.
If you just want to use it locally, wrap it in a function:
(function() {var linkObj; ... })()
However, this way nothing outside of the function will be able to access it.
If you want to explicitly share certain variables between different scripts, you could also use an object as a namespace:
var myProject = {}
myProject.linkObj = ...
This will minimize how many global names you have to rely on.
Wrap it in a closure:
<script type="text/javascript">
(function() {
var linkObj;
// Rest of your code
})();
</script>
This way no script outside your own will have access to linkObj.
Is this a safe way to store data?
This is not storing data per se, it's only declaring a variable in a script block in what I assume is an HTML page. When you reload the page in the future, it will not hold previous values.
My concern is what if a jQuery or other plug-in was to also use the variable linkObj.
That's a valid concern, like others have pointed out. However, you would expect plugins not to rely on scope outside the plug-in. This shouldn't impact a lot as good plug-in design would likely prevent this from happening.
Also if I declare my variable like this then can it also be seen by other functions in scripts located in other js files that I include?
Yes. As long as their execution is triggered after your script block gets loaded. This normally follows the order in which your script declaration appears in the page. Or regardless of the order they appear on the page if they are executed, for example, after the jQuery DOM 'ready' event.
It's common to hear that is good to avoid 'global namespace pollution', which relates to this concern. To accomplish that you can use a function to contain code, and directly invoke that function in your script block.
(function () {
var a = 1; // the scope is within the function
alert('The variable a is equal to: ' + a);
}) (); // the parenthesis invoke the function immediately
I am referencing JavaScript as follows on an HTML page:
<script type="text/javascript" src="http://code.jquery.com/jquery-1.6.1.min.js"></script>
<script type="text/javascript" src="http://code.jquery.com/mobile/1.0b1/jquery.mobile-1.0b1.min.js"></script>
<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false®ion=GB"></script>
<script type="text/javascript" src="js/shared.js"></script>
<script type="text/javascript">
$('document').ready(function() {
// In-page code: call some functions in shared.js
});
</script>
The functions defined in shared.js are not wrapped inside $('document').ready. So:
Is it safe to assume that functions defined in shared.js are available to the "in-page code"?
If I pull out the in-page code into a separate file called local.js (keeping it wrapped in $('document').ready), is it still safe to assume that functions defined in shared.js are available?
Finally, is the fact that I'm not wrapping shared.js inside $('document').ready a problem? I'm finding that if I do wrap it, its functions are no longer available to the in-page code.
The reason for question 3 is that I'm hitting this problem: Uncaught TypeError: Property ... is not a function - after page has loaded
and wondering if it is something to do with how I've organised my code.
UPDATE: Thanks for the answers. It's now clear that using $('document').ready in shared.js would remove those functions from global scope. However, I just want to clarify the original question in point 3.
Can I assume that if I do the following:
inside my in-page code, loaded inside $('document').ready, call a function from shared.js
have the function in shared.js refer to jQuery, Google Maps, or elements on my page
there will be no problems?
In other words, is it safe to assume that the page will have loaded by the time the functions inside shared.js are called, even if I'm not wrapping everything in that file inside $('document').ready?
Is it safe to assume that functions defined in shared.js are available to the "in-page code"?
Yes, As long as those functions are injected into global scope
If I pull out the in-page code into a separate file called local.js (keeping it wrapped in $('document').ready), is it still safe to assume that functions defined in shared.js are available?
Yes, As long as local.js is included after shared.js AND shared.js injects functions into global scope.
Finally, is the fact that I'm not wrapping shared.js inside $('document').ready a problem? I'm finding that if I do wrap it, its functions are no longer available to the in-page code.
Wrapping functions in document.ready takes them outside of global scope.
var foo = 4; // global
$(function() {
var bar = 5; // local
});
foo = bar; // error
You need to inject variables in global scope, this is as easy as doing
$(function() {
/* all your code */
window["SomeGlobalVariable"] = someFunctionIWantGlobal;
});
Yes
Yes
Maybe. If you wrap code in a function you will lose global access to functions defined. For the most part that's a good thing - not polluting the global namespace. You can still access these functions in the global namespace if instead of function foo(){} you do window.foo = function(){};.
This is all irrelevant however, because you either need a dom ready listener or you don't - depending on whether or not you're trying to access the dom in that code. If yes, then wrap it, if not, then don't. As mentioned, either way you can close over your code so as not to pollute the global namespace, or pollute it if you so desire.
It is safe to assume (if the definitions are not hidden inside a closure that cannot be accessed).
//shared.js
function DoThis() {}
function DoThat() {}
It will still work, just embed local.js after shared.js
<script type="text/javascript" src="js/shared.js"></script>
<script type="text/javascript" src="js/local.js"></script>
It did not work, because the functions were wrapped in a closure (the one that will be run on domready), so they are only available inside that closure
$(document).ready(function () { //this is a closure!
function DoSg() {}
//DoSg is only available inside the closure
//cannot be accessed from the outside, it's defined inside
});
Also, it is unnecessary to put function definitions into $(document).ready(). The part that matters is when you call these functions, that should be inside .ready() (well, if it involves DOM stuff or anything that should be done after page load).
Your code organisation is fine as presented. Any functions defined in "shared.js" will be available to the rest of your page, including your $('document').ready(function() block.
However, if you place the functions in shared.js within that block, then you limit the code's scope to the $('document').ready(function() (i.e. nothing else in the page can use it) -- so that's not the way to go if you want to make stuff in "shared.js" available to other parts of your code / application.
Finally, is the fact that I'm not
wrapping shared.js inside
$('document').ready a problem? I'm
finding that if I do wrap it, its
functions are no longer available to
the in-page code.
If you wrap your function inside document.ready those function are not available in the global scope, as function have local scope (I.E inside the function where they are contained)