This is a fuzzer to test the correctness of various top-level await JavaScript bundling strategies. Fuzzing is done by randomly generating module graphs and comparing the evaluation order of the bundled code with V8's native module evaluation order.
- Install dependencies with
npm ci - Run the fuzzer with
node ./fuzzer.js
"Same" here means that the bundled code behaves exactly the same as the unbundled code. "Different" here means that the bundled code behaves differently (i.e. is evaluated in a different order) than unbundled code. The same percentage means how many runs were same out of 300 total runs.
Note: Both the specification and V8/node currently have subtle bugs that cause undesirable behavior. So it's not really the case that matching V8/node 100% exactly is desirable. But it is desirable to match V8/node at least almost exactly (~99%) as the bugs are very subtle and only affect a few edge cases. Hopefully the various implementations of top-level await will converge on the same behavior in the future.
Variant: simple
- Custom module registry algorithm: ✅ Same (100% same)
- Webpack 5.75.0: ✅ Same (100% same)
- Import becomes inline await: 🚫 Different (80% same)
- Rollup 3.7.4: 🚫 Different (80% same)
- SystemJS 6.13.0: 🚫 Different (67% same)
Variant: trailing promise
- Webpack 5.75.0: ✅ Same (100% same)
- Custom module registry algorithm: 🚫 Different (100% same)
- SystemJS 6.13.0: 🚫 Different (40% same)
- Rollup 3.7.4: 🚫 Different (14% same)
- Import becomes inline await: 🚫 Different (11% same)
Variant: cyclic
- Custom module registry algorithm: 🚫 Different (99% same)
- Webpack 5.75.0: 🚫 Different (99% same)
- SystemJS 6.13.0: 🚫 Different (85% same)
- Import becomes inline await: 🚫 Different (67% same)
- Rollup 3.7.4: 🚫 Different (67% same)
Variant: cyclic, trailing promise
- Custom module registry algorithm: 🚫 Different (99% same)
- Webpack 5.75.0: 🚫 Different (99% same)
- SystemJS 6.13.0: 🚫 Different (46% same)
- Rollup 3.7.4: 🚫 Different (22% same)
- Import becomes inline await: 🚫 Different (20% same)