Week numbers are calculated based on locales. For this to properly work, the timeline must be loaded with a version of moment.js including locales.

To set a locale for the timeline, specify the option {locale: STRING}.

To set the scale to use week numbers, use for example {scale: 'week', step: 1}.

The following timeline is initialized with the 'de' locale and items are added with locally localized moment.js objects. The timeline locale can be switched to another locale at runtime. If you choose the 'en' locale, the week numbers will be calculated according to the US week calendar numbering scheme.