What is the meaning of this…“var evt=event||window.event;”

Question

What does the following mean in JavaScript?

var evt=event||window.event;

Answer 1

var evt=event||window.event;

The code above is a shortcut to a IF ELSE statement, and is equivalent to the bellow code:

var evt = "nothing valuable yet"; 
if ( event ) {
   evt = event;
} else {
  evt = window.event;
}

Two IF ELSE shortcuts in Javascript:

var resultIsTrue = true || false; // if first value is true, return first value
var resultIsFalse = true && false; // if first value is true, return second value