A sample JS to modify the list choice field options. var context = new SP.ClientContext.get_current(); var web = context.get_web(); var cldList = web.get_lists().getByTitle("Calendar"); var categoryField = cldList.get_fields().getByInternalNameOrTitle("Category"); var categoryChoiceField = context.castTo(categoryField, SP.FieldChoice); context.load(categoryChoiceField); ...

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