Share google drive file or folder by modify or add sharing and access permissions using google appscript. Google apps script share spreadsheet, docs, pdf, image etc. with the help of appscript.

Google app script change file sharing permissions with file id.

Source:

• setSharing(accessType, permissionType)
• accessType
• permissionType

Example: 
(Anyone who has the link can access and View file. No sign-in required. )

DriveApp.getFileById('File_ID').setSharing(DriveApp.Access.ANYONE_WITH_LINK, DriveApp.Permission.VIEW);