Bugfixes:

• Typescript definition file not compatible with noImplicitAny (#4017)
• ES6 classes are not supported for grid class (#3437)
• day numbers in month view should be localized (#3339)
• select helper is resizable, causes js error (#3764)
• selecting over existing select helper causes js error (#4031)
• eventOrder doesn't work on custom fields (#3950)
• aria label on button icons (#4023)
• dynamic option changes to select/overlap/allow doesn't cause rerender

Locales:

• added Georgian (#3994)
• added Bosnian (#4029)

• new settings for month/agenda/basic views (#3078):
  • columnHeaderFormat (renamed from columnFormat)
  • columnHeaderText
  • columnHeaderHtml
• TypeScript definition file (fullcalendar.d.ts) included in npm package (#3889)
• codebase using SASS, though not taking advantage of it yet (#3463)
• codebase fully ported to TypeScript / Webpack
• Afrikaans locale fix (#3862)

Bugfixes:

• render method does not re-adjust calendar dimension (#3893)
• when custom view navigates completely into hidden weekends, JS error (scheduler-375)

Other:

• in themes.html demo, fixed broken Bootswatch themes (#3917)
• moved JavaScript codebase over to TypeScript
  (same external API; embedded typedefs coming soon)

Bugfixes:

• Google Calendar event sources not calling loading callback (#3884)
• eventDataTransform w/ eventConstraint shouldn't be called during event resizing (#3859)
• navLinks would go to the previously navigated date (#3869)
• nowIndicator arrow would repeatedly render (#3872)
• fc-content-skeleton DOM element would repeatedly render on navigation in agenda view

Bugfixes:

• JSON feed event sources always requesting current page (#3865)
• multi-day events appearing multiple times in more+ popover (#3856)

Features:

• agendaEventMinHeight for guaranteeing height (#961, #3788) thx @Stafie
• columnHeader can be set to false to hide headings (#3438, #3787) thx @caseyjhol
• export all View classes (#2851, #3831)
• updateEvent, update complex attributes (#2864)
• Albanian locale (#3847) thx @alensaqe

Bugfixes:

• objects used as non-standard Event properties ignored by updateEvent (#3839)
• listDay error if event goes over period (#3843)
• validDays with hiddenDays, js error when no days active (#3846)
• json feed Event Source object no longer has url property (#3845)
• updateEvent, allDay to timed, when no end, wrong end date (#3144)
• removeEvents by _id stopped working (#3828)
• correct this context in FuncEventSource (#3848) thx @declspec
• js event not received in unselect callback when selecting another cell (#3832)

Incompatibilities:

• The viewRender callback might now be fired AFTER events have been rendered
  to the DOM. However, the eventRender/eventAfterRender/eventAfterAllRender callbacks
  will always be fired after viewRender, just as before.
• The internal Grid class (accessed via $.fullCalendar.Grid) has been removed.
  For monkeypatching, use DayGrid/TimeGrid directly.

• fixed loading trigger not firing (#3810)
• fixed overaggressively fetching events, on option changes (#3820)
• fixed event object date property being discarded (tho still parsed) (#3819)
• fixed event object _id property being discarded (#3811)

Features:

• Bootstrap 3 theme support (#2334, #3566)
  • (big thanks to @joankaradimov)
  • via themeSystem: 'bootstrap3' (the theme option is deprecated)
  • new bootstrapGlyphicons option
  • jQuery UI "Cupertino" theme no longer included in zip archive
  • improved theme switcher on demo page (#1436)
• 25% event rendering performance improvement across the board (#2524)
• console message for unknown method/calendar (#3253)
• Serbian cyrilic/latin (#3656)
• available via Packagist (#2999, #3617)

Bugfixes:

• slot time label invisible when minTime starts out of alignment (#2786)
• bug with inverse-background event rendering when out of range (#3652)
• wrongly disabled prev/next when current date outside of validRange (#3686, #3651)
• updateEvent, error when changing allDay from false to true (#3518)
• updateEvent doesn't support ID changes (#2928)
• Promise then method doesn't forward result (#3744)
• Korean typo (#3693)

Incompatibilities:

• Event Objects obtained from clientEvents or various callbacks are no longer
  references to internally used objects. Rather, they are static object copies.

• composer.js for Composer (PHP package manager) (#3617)
• fix toISOString for locales with non-trivial postformatting (#3619)
• fix for nested inverse-background events (#3609)
• Estonian locale (#3600)
• fixed Latvian localization (#3525)
• internal refactor of async systems

Bugfixes:

• stale calendar title when navigate away from then back to the a view (#3604)
• js error when gotoDate immediately after calendar initialization (#3598)
• agenda view scrollbars causes misalignment in jquery 3.2.1 (#3612)
• navigation bug when trying to navigate to a day of another week (#3610)
• dateIncrement not working when duration and dateIncrement have different units