Why does Javascript's OR return a value other than true/false?

Question

I saw this construction in order to get the browser viewport width:

function () { return window.innerWidth || document.documentElement.clientWidth || documen         


        

Answer 1

It's just the way it is by design. ||, like && is a short-circuit operator, the expressions are evaluated in order, they stop after an expression meets the criteria and yield the result of the expression. The same is true of &&:

var  myObj  = { "Test": { "Foo":"Bar" } };
var  myObj2 = { "Foo": "Bar" };

alert(myObj.Test && myObj.Test.Foo); // will alert "Bar";
alert(myObj2.Test && myObj2.Test.Foo); // will alert undefined;