[whatwg] <script> features

Jonas Sicking jonas at sicking.cc
Fri Mar 23 15:16:18 PDT 2012

On Fri, Feb 3, 2012 at 10:34 PM, Ian Hickson <ian at hixie.ch> wrote:
> On Mon, 16 Aug 2010, Jonas Sicking wrote:
>> I'd like to propose a couple of simple features to make <script>
>> elements more useful:
>> 1. document.currentScript
>> This property returns the currently executing <script>, if any. Returns
>> null if no <script> is currently executing. In the case of several
>> nested executing <script>s, it returns the innermost one. This is useful
>> for being able to pass parameters to the script by setting data-
>> attributes on the script element.
>> I think jQuery already does things that requires knowing which <script>
>> element linked to jQuery, and it approximates this property by getting
>> the last element in document.getElementsByTagName("script"), which won't
>> work reliably. Especially with features like <script async>.
> This feature is trivially implementable using the next one, so I haven't
> added it.

The whole point of this feature is to enable the js-code inside a
loaded script to use the .currentScript property in order to find the
<script> element in the DOM which loaded it. While it is trivial to
implement the .currentScript property from outside of the <script>
element, it is impossible to do so from inside the loaded script
itself. This since the script runs after the fired event.

I just ran into another example of a script which tries to figure out
which <script> element loaded it. In this case it does so by checking
which <script> element has a src attribute which contains the url it
expects to be loaded from. This causes it to fail when I load the
script from another url. In this case it was the respec.js script
available here: http://dev.w3.org/2009/dap/ReSpec.js/js/respec.js

So yes, it's trivial for pages to implement this. But it mostly
defeats the purpose if every page which wants to use a given library
has to re-implement this property. And it likely will mean that script
libraries won't be able to depend on the property since pages won't
implement it reliably enough.

/ Jonas

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