What's the difference between "javascript:;" and "javascript:" in an anchor href attribute?
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11The first has a semicolon, the second does not have.VisioN– VisioN2013-04-17 09:26:00 +00:00Commented Apr 17, 2013 at 9:26
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1wondering about similarity? both are badEjaz– Ejaz2013-04-17 09:32:29 +00:00Commented Apr 17, 2013 at 9:32
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4 Answers
Same as the difference between empty Javascript file and Javascript file with just a ;.
Nothing:
eval("");
//undefined
eval(";");
//undefined
See http://www.ecma-international.org/ecma-262/5.1/#sec-7.9.1
When, as the program is parsed from left to right, the end of the input stream of tokens is encountered and the parser is unable to parse the input token stream as a single complete ECMAScript Program, then a semicolon is automatically inserted at the end of the input stream.
So, empty file would be an invalid Program, then semicolon is inserted automatically, and it becomes equal to a Program with just a semicolon.
It just occurred to me that this is yet another case that prooves JSON is not a subset of Javascript: empty JSON is not valid:
JSON.parse("");
//SyntaxError: Unexpected end of input
eval("");
//undefined
:P
Comments
javascript: indicates the pseudo-protocol that can be used to evaluate JavaScript. So a single semicolon after it is equal to a script containing just ; which is an empty expression that does nothing. javascript: without anything else after it is an empty script that also does nothing. In both cases the return values are undefined which is important since a javascript: url returning something else would result in the page contents being replaced with whatever it returned.
However, you should not use javascript: urls at all - they are deprecated. Use onclick and either a useful href or # if there is no non-js version of the link. Remember to preventDefault the event in that case though.
6 Comments
dhblah
Thanks for your answer, I only want to correct you that page contents is not being replaced with what
javascript: returns, try javascript: 10 or javascript: 'google.com', it won't do anything.dhblah
Also I won't agree that javascript: shouldn't be used, as it's always possible that someone will forget to
return false; on onclick or function will throw an exception and you'll have a nasty and hard to figure out bug.
ThiefMaster
jsfiddle.net/ThiefMaster/MJ4nb - it is replaced with the expression's result... An exception being thrown won't be a problem if you
preventDefault() early enough (I usually do it in the first line of the event handler if it should be done unconditionally)dhblah
where is it replaced? I don't see anything, click doesn't do anything at all, nothing happens.
ThiefMaster
Maybe not all browsers do it. In firefox I end up with
10 being shown instead of the previous content. |
javascript: tells that there is a javascript statement coming rather than a link to another page. The ; is the javascript statement. However, ; won't execute anything, so this is a no-op.
Comments
javascript:; is javascript: with and additional semicolon. Apart from that, there are no differences.
