JavaScript OR (||) variable assignment explanation

Question

Given this snippet of JavaScript...

var a;
var b = null;
var c = undefined;
var d = 4;
var e = \'five\';

var f = a || b || c || d || e;

alert(f); // 4
         


        

Answer 1

This is made to assign a default value, in this case the value of y, if the x variable is falsy.

The boolean operators in JavaScript can return an operand, and not always a boolean result as in other languages.

The Logical OR operator (||) returns the value of its second operand, if the first one is falsy, otherwise the value of the first operand is returned.

For example:

"foo" || "bar"; // returns "foo"
false || "bar"; // returns "bar"

Falsy values are those who coerce to false when used in boolean context, and they are 0, null, undefined, an empty string, NaN and of course false.