Explain purpose of `e` event parameter in onEdit

Question

I have some question, hope guys can answer me. In this following function, I can't understand event 'e'. What is the 'e'? how we call the function or where's the function called? Give me some example, please!

function my_on_edit(e) {
  var s = findSheetById_(e.gridId);
  var r = e.range;
  s.getRange(r.rowStart, r.columnEnd+1).setValue( s.getName() );
}

function findSheetById_(id) {
  var sheets = SpreadsheetApp.getActive().getSheets();
  for( var i in sheets )
    if( sheets[i].getSheetId() == id )
      return sheets[i];
  throw 'Unable to find sheet with id: '+id;
}

Answer 1

Function my_on_edit is probably bound to onEdit trigger, check out Google Script triggers. List of active triggers is available in script editor in Resources menu.

On each edit action on your spreadsheet this handler is called with edit event object passed. e contain fields:

{ 
    String user, 
    SpreadSheet source, 
    Range range,
    Object value 
}

You can find more detailed description at section "Spreadsheet Edit Events"

Answer 2

You know, I had the same question: what was that "е" in onOpen(e). I found an answer right there on Google website:

The e parameter in the function names above is an event object that is passed to the function. https://developers.google.com/apps-script/guides/triggers.

And then they explain that the event object contains information about the context that caused the trigger to fire.