Show Preview before complete
Show preview before complete the survey. The functionality is disabled by default. You can optionally show all or only answered questions on the preview page:
default is 'noPreview'. 'showAllQuestions' - show all visible questions on the preview page.
'showAnsweredQuestions' - show only answered visible questions on the preview page.
If you change the property when you are in the "preview" state, preview page is showing, then this change will not take effect.
survey.showPreviewBeforeComplete = yourValue;