Are there side effects to using string concatenation or jQuery inside jquery selectors?

while exploring jQuery I came up with the following weird script. I don't see myself doing this really however concatenating strings to achieve a variable name is not unusual in JavaScript.

Any feedback welcome.

...
    <script type="text/javascript">
        var a = 'y';
        $(document).ready(function() {
            $('p[id^=' + $('p[id=x]').html() + a + "]").css('color','blue');
        });
    </script>
...

<p id="x">2a</p>
<p id="2ay_">mytext</p>

From stackoverflow

• Short answer is no, there aren't side-effects. Your example is quirky, but as you said you were just exploring to see what you could do. I have used string concatenation and function value returns inside jQuery selectors before, it can be a useful technique for managing sets of related elements which reside in different parts of the DOM.

  I admit I haven't used jQuery.html() inside a selector, but there isn't any inherent reason why that's "bad". I just can't think of a situation where that'd be strictly necessary. It does make the code rather... unusual, and hence more difficult to understand and maintain.

  If you actually find a use for this in production code, please let us know. I'd be fascinated to see what it is. :)

  Florin : Just wondering about some black magic in jQuery that would give unwanted side effects inside selectors. What I find myself needing is a to pass the 'search' string to the selector at runtime. Could by the way, jQuery do with this pattern: $('p[id=?]').click(paramValue, function() {}); ?

• In my opinion its unreadable, unmaintainable...anything like that should be avoided. Imagine you joined a new company and they put you in front of a whole bunch of js/jquery code that looked like that!!

  P.S you should use addClass to change the color. I would rather change a css class after all it is a style setting and is also more extensible in that you can add other styles without any more js code.

• No, nothing weird. Other than maybe some unwanted results if someone/you went and modified the HTML within the p element. It is definitely pretty weird the way it's coded, but nothing really wrong with it (other than being unreadable/unmaintainable).

  Because jQuery is nothing special -- it's just a Javascript library. You aren't using some special JS syntax or anything, jQuery is simply taking a string and using it as a selector. So that string can be constructed any way you see fit.

• Just wondering about some black magic in jQuery that would give unwanted side effects inside selectors. What I find myself needing is a to pass the 'search' string to the selector at runtime.

  Could by the way, jQuery do with this pattern:

  $('p[id=?]').click(paramValue, function() {}); where the paramValue replaces the placeholder '?' ?

• Yep no reason you can't do this. Since $ is actually a function call itself anything that needs to be evaluated in order to pass a parameter to it is evaluated first.