Javascript – Prevent hiding of ModalPopupExtender when ok or cancel is clicked

hmmm... I'm pretty sure that there's a shown event for the MPE... this is off the top of my head, but I think you can add an event handler to the shown event on page_load

function pageLoad()
{
    var popup = $find('ModalPopupClientID');
    popup.add_shown(SetFocus);
}

function SetFocus()
{
    $get('TriggerClientId').focus();
}

i'm not sure tho if this will help you with calling it from the server side tho

The most likely reason for use of single vs. double in different libraries is programmer preference and/or API consistency. Other than being consistent, use whichever best suits the string.

Using the other type of quote as a literal:

alert('Say "Hello"');
alert("Say 'Hello'");

This can get complicated:

alert("It's \"game\" time.");
alert('It\'s "game" time.');

Another option, new in ECMAScript 6, is template literals which use the backtick character:

alert(`Use "double" and 'single' quotes in the same string`);
alert(`Escape the \` back-tick character and the \${ dollar-brace sequence in a string`);

Template literals offer a clean syntax for: variable interpolation, multi-line strings, and more.

Note that JSON is formally specified to use double quotes, which may be worth considering depending on system requirements.