I have seen at many locations that people use javascript: before functions(classes) or using attributes? E.g., javascript:Blob, javascript:void(0).
I'm wondering what are the situation when using this notation can be necessary?
Or what're the best practices regarding using or not using this?
Expanding scope of my question:
Can it be useful to use it without href. I.e., in JS file directly?
Does ECMAScript have to do anything with it?
"javascript:" is a URL protocol. When the browser loads a javascript: URL, it takes the rest of the URL as JavaScript code and executes it. Thus, you can put this in an href attribute on an <a> tag.
It's generally better to not do this, though - instead, you can set href='#' and put your JS code in the onclick attribute. (Some recommend setting href='javascript:void(0)', which is similar but subtly different. See here.)
This is usually used for HTML a tag HREF's ie LINK TEXT
Related
I don't know why this link does not work, but I have a Javascript redirect (window.opener.location) that I am passing a number of variables through the URL and am having issues when those variables contain apostrophes. I am using URLENCODE() in PHP to build the link, which looks like it is doing what I need when I dump the source, but Safari and Chrome both throw "Unexpected identifier at 'www'" errors when I click the link.
This seems to tell me that the JS link is still being treated as if it has an apostrophe instead of the %27 equivalent of an apostrophe? I am using a dummy name "qqq'www qqq'www" with apostrophes in first and last name for my testing to break as much stuff as possible.
Here is the link I am having trouble with:
<em>Yes</em>
But if I change the link to use onclick instead of the HREF, it works? I realize this is the better coding method than href='javascript:...' too.
<em>Yes</em>
Everything is identical except where I make the JS call. Is this possibly due to the way the HREF and onclick are handled on encoding/decoding? Maybe the HREF is un-encoding the apostrophes prior to making the link call because the JS is embedded in the HREF call?
Any insight into this behavior would be appreciated so I can better understand what is really going on here. Yes it works, but not knowing why makes me feel like a worse developer...
Thanks!
Your links do not have a > to end the starting <a - and yes, do not use href="javascript:
Also if you need to encode, use encodeURIComponent and lastly do not try to close the window before changing the opener.
But why not name the opener and user a target and a setTimeout?
<a target="nameOfOpener"
href="../cust/maint_cust.php?action=del_are_you_sure&cust_id=249735&lname=Qqq%27www&fname=Qqq%27www"
onclick="setTimeout(function() {top.close()},100)"><em>Yes</em></a>
Browsers give a special treatment to href attributes starting with 'javascript:'. Any %xy encoding, as in your case the %27, will be decoded first before executing the Javascript code. I checked this for current versions of Firefox and Chrome. I would be curious to find a documentation of this feature.
The short answer is: Do not use 'javascript:' in a href, if your Javascript code contains %xy encodings.
In case you really have to use 'javacript:' in a href, put your URL into a javascript variable and then reference that variable in your href's Javascript code.
<script>
myURLwithEncodings = "../cust/maint_cust.php?action=del_are_you_sure&cust_id=249735&lname=Qqq%27www&fname=Qqq%27www";
</script>
<em>Yes</em>
This question already has answers here:
What's the point of "javascript:" in code (not URLs)? [duplicate]
(4 answers)
Closed last year.
A lot of the time I see people calling javascript functions using colon (:).
Like onclick="javascript:functionname();"
The same function works without javascript: and I'm curious to know when to use javascript: and when not to.
Any suggestions are appreciated.
javascript: prefix is extremely important when you put code to anchor href attribute:
Anchor
Whereas in inline event attributes (like onclick, onsubmit, onmouseover, etc.) javascript: prefix is not important.
However, you should note that both approaches given here are not good to implement and you should use alternative ways (e.g as #Paul S. stated in the comments)
This is not as commonly seen in onclick events as these events already execute javascript. You will may see something like the following quite a bit:
Link
The reason for such code is that by default an href attribute is trying to change the location or redirect. This tells the browser that the default href action will be javascript that is run. Otherwise, the function will not run and the page will refresh which is quite annoying.
Page refreshing is a common issue when using javascript like this in an anchor tag since an anchor tags default action is to refresh or load another page. The return false; at the end signals that the default action (i.e. refresh or load) should not fire.
Hope this helps.
I believe the javascript: prefix is left over from when there were many other script types bouncing around on the web (vbScript, for example) and in order to differentiate between them in HTML you needed to provide these prefixes.
That being said, these tags do absolutely nothing in any browser other then IE anymore, and even in IE you generally can omit them.
Also notice that this entire question is moot since you should be binding event handlers through javascript, not in HTML.
Is the javascript: prefix really needed? I know you should aim for unobtrusive JavaScript but under what circumstances would something break if it is not there?
javascript: is a URI scheme.
It is needed to create a URI that runs Javascript, either in an href="" attribute or in the browser address bar.
There is never a situation in which javascript: is optional.
Best practices indicate that javascript: URIs should be avoided where possible in favor of click handlers, so its use is frowned upon.
However, there are cases where there is no alternative. For example, bookmarklets can only be created by using javascript:.
They're "needed" if you are encoding Javascript code into an URI, for example in the href property of an <a> tag.
They're bad practice, though.
If you put JavaScript code into the href attribute of an a, or other attribute which takes a URL, then it's required for the browser to detect that it is JS. It's not necessary (and may not even work) if you use it with onclick or other attributes that already expect JS code.
That "prefix" is used only in the href attribute of an html anchor (). It is never actually needed, since you could as well define a click event handler.
It is needed even in onclick situations if you also have a VBS routine on the same page.
Is there a way in JavaScript to get the contents of a linked file without making a second GET request? That is, if I have
<link rel="foo" href="bar.txt">
the browser should automatically download bar.txt. Is there any way to read its contents without getting it again (i.e. via jQuery's $.get or similar)?
Edit
I could use a second GET request and as mentioned in the comments there likely wouldn't be a performance hit, but this question is mainly a thought experiment: it seems like it'd be pretty standard functionality, but more and more things point to this not being possible. Is there a reason why?
If the tag has absolutly no other purpose than being a placeholder for the source, then the objective is to prevent the first get rather then the second ;) By using another attribute you avoid the default behaviour.
<link data-src='file.txt' />
'data-...' is a valid HTML5 attribute you can use right now, though the html will not be valid if an older doctype is declared but will still work.
Next when using jQuery:
$('link[data-src]').each(function(){
var self = $(this)
, src = self.attr('data-src');
$.get(src, function(fileContent){
// do stuff with fileContent
})
});
Obviously any element will do rather then the link element when using 'data-...', I use this technique myself to add data in a component based architecture, lazily binding resources and meta information to components without it affecting default behaviours/renditions.
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).