I am looking for a solution similar to: How to Call "Open with Explorer" From Custom Code? and http://sharepoint.hannahswain.eu/2013/04/26/using-the-open-in-explorer-link-on-sharepoint-2013/
but for Online version.
When I am trying to use Script Editor web part and insert the code above, SPO seems to "eat up" part of the code, so I am guessing it does not comply with the security measures/sandbox solutions model.
When inspecting the element on the default "Open in Explorer" button, I get this:
'Command':'OpenWithExplorer','ClickScript':'CoreInvoke\\u0028\\u0027NavigateHttpFolder\\u0027,\\u0027https:\\\\u002f\\\\u002ftenant.sharepoint.com\\\\u002fsites\\\\u002fTeamsitewithLibraries\\\\u002fShared Documents\\u0027, \\u0027_blank\\u0027\\u0029;','HiddenScript':'!\\u0028SupportsNavigateHttpFolder\\u0028\\u0029\\u0029','LabelText':'Open with Windows Explorer','Description':'Drag and drop files into this library.'
so the function does seem to be similar, judging by the parameters.