A basic jQuery examination

An email I sent to iiNet earlier this evening. It bounced: Sorry, no mailbox here by that name. (#5.1.1) ; so posting it here instead!


Hi there,

Thought I would give you a heads up on a bug I found on your site.

My BoB2 modem stopped working earlier this evening - it appears to have done a factory reset of itself without me asking it to.

That led me to get redirected to https://toolbox.iinet.net.au/cgi-bin/playpen/boblogin.cgi when I visited any page. I submitted the login form, as requested by the page, and absolutely nothing happened - no network activity.

Thus I began to investigate, while waiting on the line for tech support.

You will find below part of the HTML markup, and part of the main Javascript file that was loaded.

HTML:

<div>
    <p id="username_prompt">
        Username: <input type="text" name="username" id="boblogin_username" maxlength="50" size="30">
    </p>
    <p id="password_prompt">
        Password: <input type="password" name="password" id="boblogin_password" maxlength="50" size="30">
    </p>
    <div id="boblogin_result"></div>
    <p>
        <input type="button" id="login_button" class="toolbox_button" value="configure">
        <br><br><span id="loading_image" style="display: none;"><img id="loading_image" src="https://toolbox.iinet.net.au/images/Throbber.gif"></span>
    </p>
    <p>
        <a href="https://toolbox.iinet.net.au/cgi-bin/playpen/9pointidcheck.cgi" target="__blank">Forgot login details?</a>
    </p>
</div>

Javascript:

init = function() {
    $('login_button').onclick = function() { checkLogin(); };
};

Quickly spotted the bug - if I run:

$('login_button')
[]

If I run instead:

$('#login_button')
[<input type="button" id="login_button" class="toolbox_button"
value="configure">]

It thus appears that $ is jQuery, and you have simply omitted the # in the selector. This is required whenever selecting based on id attributes.

That was the main bug, which prevented this page from working.

Further to that, I would suggest a few more improvements.

Again, the same function:

init = function() {
    $('login_button').onclick = function() { checkLogin(); };
};

Firstly, wrapping checkLogin in a function is extraneous, you could do instead:

$('#login_button').onclick = checkLogin;

… as checkLogin is itself a function.

In idiomatic jQuery:

$('#login_button').click(checkLogin);

Secondly init is declared without using var, and thus pollutes the global scope. This is bad practice, and the init function is not the only offender here - all of the functions in this file do the same. On a relatively simple page like this, it makes little difference, but should it get more complex, this can cause weird side effects. Consider not only using var, but also placing these functions within a scope. A rather nice explanation: http://stackoverflow.com/a/13352212/194982

Finally, this init function is invoked from the HTML markup using:

<script type="text/javascript">
    init();
</script>

One cannot guarantee that the contents of this script tag will be run after the DOM is rendered. If it so happens that this runs before the DOM is rendered, the selector will return an empty set, and the click handler will not be set on the intended button.

Consider instead using:

$(document).ready(init);

… within the Javascript file. The additional benefit of this is that we do not need any in line scripts defined in the markup.

Cheers, Brendan

Copyright © 2008-present Brendan Graetz