QGIS/resources/function_help/json/to_date

{
  "name": "to_date",
  "type": "function",
  "description": "Convert a string into a date object. An optional format string can be provided to parse the string; see <a href='https://doc.qt.io/qt-5/qdate.html#fromString-1'>QDate::fromString</a> for additional documentation on the format.",
  "arguments": [ 
   {"arg":"string","description":"string representing a date value"},
   {"arg":"format","optional":true,"description":"format used to convert the string into a date"}
  ],
  "examples": [ 
   { "expression":"to_date('2012-05-04')", "returns":"2012-05-04"},
   { "expression":"to_date('June 29, 2019','MMMM d, yyyy')", "returns":"2019-06-29"}
  ]
}