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Is it possible to find out (in Chrome/FireFox) that which Javascript file (and hopefully line number) is being used on a web page by a specific element?
Thanks
The question is a bit unclear, but I can show you how to watch a particular element for JavaScript interaction in Chrome:
Then, after you do that, watch as we click the checkbox:
Some reference for Chrome: https://developers.google.com/chrome-developer-tools/docs/overview
Most other browser work in a similar fashion. There are also other ways to find out how JavaScript code is interacting with your page, but you'll need to give me a more specific scenario to answer that.
I am using firebug to edit my magento theme. In a particular element I am getting an element.style attribute that I want to edit. Now how do I know which JS file is to be edited?
If you want to interact with elements via Javascript, you can use the console function in Firebug. Go to console, and click enable and from there you can start typing code as if it were javascript.
Example, if you wanted to check the z-index property of a specific element you could just type the javascript in the console:
document.getElementById("idOfElement").style.z-index
and when you hit enter it should tell you. You can also see errors in the javascript file if there are any.
If you are looking for the Javascript file of what is committing this change in the z-index property and you are 100% certain it is because of the Javascript, then you can use the debugger Firebug has which is also in the Scripts tab. If you're dealing with multiple javascript files, I'm not entirely sure how you can sift through which JS file is causing it, I believe you'll have to do that digging on your own. The debugger allows you step through your JS file though and see what changes are being made step-by-step.
Here is a tutorial on how to use the debugger if you're not familiar. Hope this helps.
Not sure about firebug,
But if you use linux you may try this command,
grep "element.style" -Rn .
Do you Want to change the Style or Something other.
If you want to change Style of a Particular Element, Just Follow the Steps
F12
Select Inspect Tool
Click on the Element where you want to change
In a FireBug Window look at Right and Make Sure style Tab is Selected
Just Single Click on value of a Particular Property
If you are not finding solution, Please Determine the Problem bit Clearly.
So, I've written a little javascript widget. All a user has to do is paste a script tag into the page, and right below it I insert a div with all of the content the user has requested.
Many sites do similar things, such as Twitter, Delicious and even StackOverflow.
What I'm curious about is how to test this widget to make sure that it will work properly on everyone's webpage. I'm not using an iframe, so I really want to make sure that this code will work when inserted most places. I know it looks the same in all browsers.
Suggestions? Or should I just build one hundred web pages and insert my script tag and see if it works? I would hope there is an easier way than that.
Once you have confirmed that your javascript works cross-browser in a controlled environment, here are some things that might cause problems when used on an actual website:
CSS
You're using a CSS class that is already being used (for a different purpose) by the target website
You're using positioning that might interfere with the site's CSS
The elements you are using are being styled by the website's CSS (you might want to use some sort of "reset" CSS that applies only to your widget)
HTML
You're creating elements with the same id attribute as an element that already exists on the website
You're specifying a name attribute that is already being used (while name can be used for multiple elements, you may not be expecting that)
Javascript
What is the expected behaviour without Javascript enabled? If your script creates everything, is it acceptable for nothing to be present without JS?
At very basic you should make sure your widget works for following test-cases. I am sure then it will work on all web-pages -
http/https: There should not be any warning for HTTPS pages for unencrypted content.
<script> / <no-script>: What if JavaScript is disabled? Is your widget still visible?
What happens when third-party cookies are disabled? Does your widget still work?
Layout-box restrictions: When parent div element's size is less than your widget. Does your widget overflow the given size and destroys owners page?
By keeping all your Javascripts under a namespace (global object) with a very unique name, you should be pretty much OK. Also, you can simply use an anonymous function if you just want to print out something.
Similar question: How to avoid name clashes in JavaScript widgets
In the 1990s, there was a fashion to put Javascript code directly into <a> href attributes, like this:
Press me!
And then suddenly I stopped to see it. They were all replaced by things like:
Press me!
For a link whose sole purpose is to trigger Javascript code, and has no real href target, why is it encouraged to use the onclick property instead of the href property?
The execution context is different, to see this, try these links instead:
Press me! <!-- result: undefined -->
Press me! <!-- result: A -->
javascript: is executed in the global context, not as a method of the element, which is usually want you want. In most cases you're doing something with or in relation to the element you acted on, better to execute it in that context.
Also, it's just much cleaner, though I wouldn't use in-line script at all. Check out any framework for handling these things in a much cleaner way. Example in jQuery:
$('a').click(function() { alert(this.tagName); });
Actually, both methods are considered obsolete. Developers are instead encouraged to separate all JavaScript in an external JS file in order to separate logic and code from genuine markup
http://www.alistapart.com/articles/behavioralseparation
http://en.wikipedia.org/wiki/Unobtrusive_JavaScript
The reason for this is that it creates code that is easier to maintain and debug, and it also promotes web standards and accessibility. Think of it like this: Looking at your example, what if you had hundreds of links like that on a page and needed to change out the alert behavior for some other function using external JS references, you'd only need to change a single event binding in one JS file as opposed to copying and pasting a bunch of code over and over again or doing a find-and-replace.
Couple of reasons:
Bad code practice:
The HREF tag is to indicate that there is a hyperlink reference to another location. By using the same tag for a javascript function which is not actually taking the user anywhere is bad programming practice.
SEO problems:
I think web crawlers use the HREF tag to crawl throughout the web site & link all the connected parts. By putting in javascript, we break this functionality.
Breaks accessibility:
I think some screen readers will not be able to execute the javascript & might not know how to deal with the javascript while they expect a hyperlink. User will expect to see a link in the browser status bar on hover of the link while they will see a string like: "javascript:" which might confuse them etc.
You are still in 1990's:
The mainstream advice is to have your javascript in a seperate file & not mingle with the HTML of the page as was done in 1990's.
HTH.
I open lots of links in new tabs - only to see javascript:void(0). So you annoy me, as well as yourself (because Google will see the same thing).
Another reason (also mentioned by others) is that different languages should be separated into different documents. Why? Well,
Mixed languages aren't well supported
by most IDEs and validators.
Embedding CSS and JS into HTML pages
(or anything else for that matter)
pretty much destroys opportunities to
have the embedded language checked for correctness
statically. Sometimes, the embedding language as well.
(A PHP or ASP document isn't valid HTML.)
You don't want syntax
errors or inconsistencies to show up
only at runtime.
Another reason is to have a cleaner separation between
the kinds of things you need to
specify: HTML for content, CSS for
layout, JS usually for more layout
and look-and-feel. These don't map
one to one: you usually want to apply
layout to whole categories of
content elements (hence CSS) and look and feel as well
(hence jQuery). They may be changed at different
times that the content elements are changed (in fact
the content is often generated on the fly) and by
different people. So it makes sense to keep them in
separate documents as well.
Using the javascript: protocol affects accessibility, and also hurts how SEO friendly your page is.
Take note that HTML stands for Hypter Text something something... Hyper Text denotes text with links and references in it, which is what an anchor element <a> is used for.
When you use the javascript: 'protocol' you're misusing the anchor element. Since you're misusing the <a> element, things like the Google Bot and the Jaws Screen reader will have trouble 'understanding' your page, since they don't care much about your JS but care plenty about the Hyper Text ML, taking special note of the anchor hrefs.
It also affects the usability of your page when a user who does not have JavaScript enabled visits your page; you're breaking the expected functionality and behavior of links for those users. It will look like a link, but it won't act like a link because it uses the javascript protocol.
You might think "but how many people have JavaScript disabled nowadays?" but I like to phrase that idea more along the lines of "How many potential customers am I willing to turn away just because of a checkbox in their browser settings?"
It boils down to how href is an HTML attribute, and as such it belongs to your site's information, not its behavior. The JavaScript defines the behavior, but your never want it to interfere with the data/information. The epitome of this idea would be the external JavaScript file; not using onclick as an attribute, but instead as an event handler in your JavaScript file.
Short Answer: Inline Javascript is bad for the reasons that inline CSS is bad.
The worst problem is probably that it breaks expected functionality.
For example, as others has pointed out, open in new window/tab = dead link = annoyed/confused users.
I always try to use onclick instead, and add something to the URL-hash of the page to indicate the desired function to trigger and add a check at pageload to check the hash and trigger the function.
This way you get the same behavior for clicks, new tab/window and even bookmarked/sent links, and things don't get to wacky if JS is off.
In other words, something like this (very simplified):
For the link:
onclick = "doStuff()"
href = "#dostuff"
For the page:
onLoad = if(hash="dostuff") doStuff();
Also, as long as we're talking about deprecation and semantics, it's probably worth pointing out that '</a>' doesn't mean 'clickable' - it means 'anchor,' and implies a link to another page. So it would make sense to use that tag to switch to a different 'view' in your application, but not to perform a computation. The fact that you don't have a URL in your href attribute should be a sign that you shouldn't be using an anchor tag.
You can, alternately, assign a click event action to nearly any html element - maybe an <h1>, an <img>, or a <p> would be more appropriate? At any rate, as other people have mentioned, add another attribute (an 'id' perhaps) that javascript can use as a 'hook' (document.getElementById) to get to the element and assign an onclick. That way you can keep your content (HTML) presentation (CSS) and interactivity (JavaScript) separated. And the world won't end.
I typically have a landing page called "EnableJavascript.htm" that has a big message on it saying "Javascript must be enabled for this feature to work". And then I setup my anchor tags like this...
<a href="EnableJavascript.htm" onclick="funcName(); return false;">
This way, the anchor has a legitimate destination that will get overwritten by your Javascript functionality whenever possible. This will degrade gracefully. Although, now a days, I generally build web sites with complete functionality before I decide to sprinkle some Javascript into the mix (which all together eliminates the need for anchors like this).
Using onclick attribute directly in the markup is a whole other topic, but I would recommend an unobtrusive approach with a library like jQuery.
I think it has to do with what the user sees in the status bar. Typically applications should be built for failover in case javascript isn't enabled however this isn't always the case.
With all the spamming that is going on people are getting smarter and when an email looks 'phishy' more and more people are looking at the status bar to see where the link will actually take them.
Remember to add 'return false;' to the end of your link so the page doesn't jump to the top on the user (unless that's the behaviour you are looking for).
I have been using a noscript tag to show a warning when users have JavaScript disabled or are using script blocking plugins like Noscript. The website will not function properly if JavaScript is disabled and users may not figure out why it is not working without the warning.
After the latest Google algorithm shuffle, I have seen the daily traffic drop to about 1/3 of what it was in the previous months. I have also seen pages that were ranking #1 or #2 in the SERPS drop out of the results. After doing some investigating in webmaster tools, I noticed that "JavaScript" is listed as #16 in the keywords section. This makes no sense because the site has nothing to do with JavaScript and the only place that word appears is in the text between the noscript tags.
It seems that Google is now including and indexing the content between the noscript tags. I don't believe that this was happening before. The warning is three sentences. I'd imagine that having the same three sentences appearing at the top of every single page on the site could have a damaging effect on the SEO.
Do you think this could be causing a problem with SEO? And, is there any other method to provide a warning to users who have JavaScript disabled in a way that won't be indexed or read by search engines?
Put the <noscript> content at the end of your HTML, and then use CSS to position it at the top of the browser window. Google will no longer consider it important.
Stack Overflow itself uses this technique - do a View Source on this page and you'll see a "works best with JavaScript" warning near the end of the HTML, which appears at the top of the page when you switch off JavaScript.
<noscript> is not meant for meaningless warnings like:
<noscript>
Oh, no! You don't have JavaScript enabled! If you don't enable JS, you're doomed. [Long explanation about how to enable JS in every browser ever made]
</noscript>
It's meant for you to provide as much content as you can, along with a polite mention that enabling JS will provide access to certain extra features. You'll find that basically every popular site follows this guideline.
I don't think using <noscript> is a good idea. I've heard that it is ineffective when the client is behind a JavaScript-blocking firewall - if the client's browser has JavaScript enabled the <noscript> tag won't activate, because, as far as the browser's concerned, JavaScript is fully operable within the document...
A better method IMO, is to have all would-be 'noscript' content hidden by JavaScript.
Here's a very basic example:
...
<body>
<script>
document.body.className += ' js-enabled';
</script>
<div id="noscript">
Welcome... here's some content...
</div>
And within your StyleSheet:
body.js-enabled #noscript { display: none; }
More info:
Replacing <noscript> with accessible, unobtrusive DOM/JavaScript
Reasons to avoid NOSCRIPT
Somebody on another forum mentioned using an image for the warning. The way I see it, this would have three benefits:
There wouldn't be any irrelevant text for search engines to index.
The code to display a single image is less bulky than a text warning (which gets loaded on every page).
Tracking could be implemented to determine how many times the image is called, to give an idea of how many visitors have JavaScript disabled or blocked.
If you combine this with something like the non-noscript technique mentioned by J-P, it seems to be the best possible solution.
Just wanted to post an interesting tidbit related to this. For a site of mine I have ended up doing something similar to what stack overflow uses, but with the addition of a "find out more" link as my users are not as technical as this site.
The interesting part is that following advice of people aboce, my solution ditched the noscript tag, instead opting to hide the message divs with javascript. But I found that if firefox is waiting for its master password, this hiding of the message is interupted, so I think I will go back to noscript.
If you choose a solution based on replacing the div content (if js is enabled, then the div content gets updated) rather than using a noscript tag, be careful about how google views this practice:
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=66353
I'm not sure google will consider it deceptive, but it's something to consider and research further. Here's another stackoverflow post about this: noscript google snapshot, the safe way