Control-click the flags to (de)select multiple flags.
The --big-transactions flag is important for two
of the bigger tests. Without it, those tests create a
combined total of 140k implicit transactions, reducing their
speed to an absolute crawl, especially when WASMFS is
The easiest way to try different optimization levels is,
from this directory:
$ rm -f jswasm/speedtest1.js; make -e emcc_opt='-O2' speedtest1
Then reload this page. -O2 seems to consistently produce the fastest results.