[modern]
# Modern builds target recent browsers supporting the latest features to minimize transpilation, polyfills, etc.
# It is served to browsers meeting the following requirements:
# - released in the last year + current alpha/beta versions
# - Firefox extended support release (ESR)
# - with global utilization at or above 0.5%
# - must support dynamic import of ES modules
# - exclude browsers no longer being maintained
# - exclude KaiOS, QQ, and UC browsers due to lack of sufficient feature support data
unreleased versions
last 1 year
Firefox ESR
>= 0.5% and supports es6-module-dynamic-import
not dead
not KaiOS > 0
not QQAndroid > 0
not UCAndroid > 0

[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 at or 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

[legacy-sw]
# Same as legacy plus supports service workers
unreleased versions
last 7 years
>= 0.05% and supports websockets and supports serviceworkers