These docs are for an old release. Info on upgrading to v4
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weekMode

Determines the number of weeks displayed in a month view. Also determines each week’s height.

This method has been removed in v3. In its place, use fixedWeekCount, which controls the number of rows, and the height/contentHeight settings, which can be set to "auto".

String, default: 'fixed'

Available options:

'fixed'
The calendar will always be 6 weeks tall. The height will always be the same, as determined by height, contentHeight, or aspectRatio. Use fixedWeekCount as true instead.
'liquid'
The calendar will have either 4, 5, or 6 weeks, depending on the month. The height of the weeks will stretch to fill the available height, as determined by height, contentHeight, or aspectRatio. Use fixedWeekCount as false instead.
'variable'
The calendar will have either 4, 5, or 6 weeks, depending on the month. Each week will have the same constant height, meaning the calendar’s height will change month-to-month. Use height as "auto" and fixedWeekCount as false instead.