IE11 support broken due to emscripten issue

[tomdrewes]

I noticed that I was seeing an "Object expected" error in sass.worker.js when running on IE11. It appears there is an issue in recent versions of emscripten that is causing this:

emscripten-core/emscripten#6204

They cite passing the -s LEGACY_VM_SUPPORT=1 to emcc as a workaround. I've tested this and it does work. Apparently, there is also an open pull request to incorporate a fix into default emscripten output.

Just wondered if in the interim it might make sense to add the LEGACY_VM_SUPPORT flag to libsass/Makefile.patch in order to restore IE11 support.

[rodneyrehm]

Thanks for not only reporting a problem but also figuring out the solution!

I'm currently looking into getting libsass 3.5.0 to work on top of 0.11.0-beta.1 which switches to WebAssembly. Does the IE11 problem also occur in that version? would -s LEGACY_VM_SUPPORT=1 also solve the problem there?

[rodneyrehm]

Nevermind… IE11 doesn't like the current WASM build at all :D

no native wasm support detected
no binaryen method succeeded. consider enabling more options, like interpreting, if you want that: https://github.com/kripken/emscripten/wiki/WebAssembly#binaryen-methods

[tomdrewes]

I discovered the same. :-)

IE11 doesn't support native WebAssembly:
https://caniuse.com/#feat=wasm

And running a build from 0.11.0-beta.1 on IE11 results in the following error:
no native wasm support detected
SCRIPT0: abort("no binaryen method succeeded. consider enabling more options, like interpreting, if you want that: https://github.com/kripken/emscripten/wiki/WebAssembly#binaryen-methods"). Build with -s ASSERTIONS=1 for more info.
sass.worker.js (5,1)

It appears that for webasm to work, you'll have to define some alternative binary loading method to support IE11:
https://github.com/kripken/emscripten/wiki/WebAssembly#binaryen-methods

If the alternative was asm.js, I'd imagine the same LEGACY_VM_SUPPORT flag would apply.

[rodneyrehm]

alright, as 3.5.0 seems to work without a problem I guess it's IE11 time…

[rodneyrehm]

Hey @tomdrewes, sorry for the insane delay. I've added the flag and released 0.10.11.

[tomdrewes]

Thanks for the fix @rodneyrehm. The change works on my setup, however, the upgrade to emscripten 1.38.12 seems to have added another IE/Edge wrinkle for web workers. I'll just briefly summarize here in case anyone else runs into the issue:

The loader for emscripten in sass.worker.js tries to create a "random_device" from which it can summon random numbers. It derives this from the crypto API which comes in various flavors via the window object and for some web workers via self. Unfortunately, IE and Edge do not support crypto (nor the prefixed msCrypto) on web workers (https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/7607496/). In earlier versions of emscripten, it appears the loader would just patch in a pseudo-random number generator (not cryptographically secure, which may have been the reason for changing things in the more recent emscripten release) but in the current version, if it can't find the crypto API, it aborts with a message similar to the following:

random_device

SCRIPT0: 6439624
sass.worker.js (5,1)

As a workaround in my application I am prepending a shim on sass.worker.js for missing crypto which does basically this (some details omitted):

if (!self.crypto) {
    self.crypto = {
        getRandomValues: function(array) {
            for (var i = 0, l = array.length; i < l; i++) {
                array[i] = Math.floor(Math.random() * 256
            }
            return array;
        }
    };
}

This is, of course, not cryptographically secure, so one should not use this in an application that depends on such properties! I do not see any references to random_device in the rest of the sass.worker.js code, however, so this seems like a reasonably safe approach.

[Johann-S]

Thanks @tomdrewes for you fix, but It fix the issue only for Edge and not IE 11.

I would like to know if we'll have an official solution for that issue ? (I'm facing too)