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Boolean

A Boolean value is either 'true' or 'false'. A Boolean variable can be initialized with a primitive Boolean value or a Boolean object.

The following all evaluate to 'false': false, 0,-0, null, undefined, NaN, “”, document.all

All other values evaluate to 'true'.

Do not confuse the primitive Boolean values 'true' and 'false' with a Boolean object.


var a = new Boolean(false);
var b = false;

if (a) console.log("a");
if (b) console.log("b");
if (!0) console.log("!0");
if ("0") console.log("0");
if ([]) console.log("[]");
if ({}) console.log("{}");
if (document.all) console.log("document.all");

a !0 0 [] {}
This roughly converts a string to a Boolean primitive.
String(s).toLowerCase() == 'true'