On 06/25/2014 05:40 PM, Robert O'Callahan wrote:
On Thu, Jun 26, 2014 at 8:06 AM, Jason Orendorff
<jorendo...@mozilla.com <mailto:jorendo...@mozilla.com>> wrote:
An alternative involves letting you modify JS code just before
it's compiled (source-to-source transformation). This is more
general (you could modify the instrumented code arbitrarily, and
react synchronously as it executes) but maybe that's undesirable.
It's not clear that transformed source would interact nicely with
other tools, like the debugger. And a usable API for this is a
tall order.
Why is a usable S2S API difficult to produce?
A while ago I spent a few years doing dynamic analysis of Java code.
Although the VMs had a lot of tracing and logging hooks, bytecode
instrumentation was always more flexible and, done carefully, almost
always more performant. I had to write some libraries to make it easy
but tool builders enjoy writing and reusing those :-).
I meant "usable" in the Donald Norman sense. The underlying
source-transformation hook could be quite simple, and yet completely
beyond the people who actually have a use for it. How many potential
users are willing and ready to munge ASTs by hand?
Bug 884602 contains a patch for the hook alone. I'd love to
- land that patch (it needs tests)
- write an addon that makes it easy to play with instrumentation of
content JS
- post a video demoing it
But it's very hard to justify doing that instead of, say, ES6 classes.
-j
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