[modern]
# Support for dynamic import is the main litmus test for serving modern builds.
# Although officially a ES2020 feature, browsers implemented it early, so this
# enables all of ES2017 and some features in ES2018.
supports es6-module-dynamic-import

# Exclude Safari 11-12 because of a bug in tagged template literals
# https://bugs.webkit.org/show_bug.cgi?id=190756
# Note: Dropping version 11 also enables several more ES2018 features
not Safari < 13
not iOS < 13

# Exclude KaiOS, QQ, and UC browsers due to lack of sufficient feature support data
# Babel ignores these automatically, but we need here for Webpack to output ESM with dynamic imports
not KaiOS > 0
not QQAndroid > 0
not UCAndroid > 0

# Exclude unsupported browsers
not dead

[legacy]
# Legacy builds are served when modern requirements are not met and support browsers:
# - released in the last 7 years + current alpha/beta versionss
# - with global utilization above 0.05%
# The lattermost query ensures that support for popular old browsers is not dropped too early
# (e.g. IE 11, Android 4.4, or Samsung 4).
#
# In addition, legacy browsers must support some minimum features that cannot be polyfilled:
# - ES5 (strict mode)
# - web sockets to communicate with backend
# - inline SVG used widely in buttons, widgets, etc.
# - custom events used for most user interactions
# - CSS flexbox used in the majority of the layout
# Nearly all of these are redundant with the above rules.
# As of May 2023, only web sockets must be added to the query.
unreleased versions
last 7 years
> 0.05% and supports websockets