[Development] Proposed syntax change for pragmas and imports in QtQuick .js files

Wed Feb 18 12:42:27 CET 2015

Hi,

We need a syntax that allows determining the dependencies unambiguously from the AST. ES 6 module import syntax allows for that, Qt.import doesn't unfortunately.

Simon

From: Chris Adams
Sent: Tuesday, February 17, 2015 09:31
To: Mike Verdone
Cc: development at qt-project.org
Subject: Re: [Development] Proposed syntax change for pragmas and imports in QtQuick .js files

Hi,

On Mon, Feb 16, 2015 at 11:34 PM, Mike Verdone <mike.verdone at ableton.com<mailto:mike.verdone at ableton.com>> wrote:
Hi all,

This is my first post to the Qt dev list. Apologies if I say something
dumb.

I'd like to propose some changes to the "meta" syntax in QtQuick .js
files. I propose this in order to support JavaScript tools such as linters
and "transpilers". Specifically I'd like to change:

.pragma singleton

to

"pragma singleton";

and

.import "foo.js" as Foo

to

var Foo = Qt.import("foo.js");

This one is a bit tricky, as that sort of statement "looks" like it could be placed anywhere within a given imperative scope, but for .js files in QML we'd probably require that such such import only occur at the start of the file (otherwise such a statement might require invalidation of the evaluation scope, recompilation of the unit, triggering of all bindings which reference the import, and so on).

On the other hand, it would have one major advantage: being able to inject symbols into the initial evaluation scope of the import at import time, via: var Foo = Qt.import("foo.js", { "Window": someObj, "Image": function() { ... } }); etc, which is something which cannot be done right now, and, in my opinion, is the biggest barrier to adding support for the vast majority of 3rd party JS libraries in QML.

We really should add support for "pragma threaded" again, too.

Cheers,
Chris.

In the first example, the pragma is changed to something that standard
JavaScript can parse and ignore. It matches nicely with the ECMAScript
"use strict"; syntax.

For the import statement, I could also apply the same string-like syntax
trick, but building an actual Qt.import function allows programs to detect
that the new variable is available in the global scope.

The "." meta syntax should be preserved for backwards compatibility.

Making these changes opens QtQuick's JS to a whole new world of JavaScript
libraries and tools. For instance, .js files can be validated with ESLint
for correctness. Tools like the 6to5 allow one to write ES6 JavaScript
right now, and transpile it to QtQuick-compatible ES5 JavaScript.

I'm not expecting any of you busy Qt developers to take on this work. I'm
just curious if these changes might be accepted if I manage to implement
them, or if you have other ideas for how to enable tools like linters to
process QtQuick JS.

Thanks,

Mike.

-
Mike Verdone
Ableton AG
Schoenhauser Allee 6-7
10119 Berlin, Germany

Vorstand: Gerhard Behles, Jan Bohl, Bernd Roggendorf
Aufsichtsrat: Uwe Struck (Vorsitzender)
Sitz: Amtsgericht Berlin-Charlottenburg HRB 72838
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