//For example, these all evaluate to false.
console.log( null ? true : false ); // false
console.log( 0 ? true : false ); // false
console.log( "" ? true : false ); // false
console.log( false ? true : false ); // false
console.log( NaN ? true : false ); // false
console.log( undefined ? true : false ); // false
//using the not operator ! on these will evaluate true
console.log( !null ); // true
console.log( !0 ); // true
console.log( !"" ); // true
console.log( !false ); // true
console.log( !NaN ); // true
console.log( !undefined ); // true
//But all the values are not equal to false
console.log( null == false ); // false
console.log( 0 == false ); // true
console.log( "" == false ); // true
console.log( false == false ); // true
console.log( NaN == false ); // false
console.log( undefined == false ); // false
//For null == false , problem here is type coercion ,typeof null is object and typeof false is boolean.
//There is no coercion under which objects of the null and boolean types can be equal, which is why this is false.
//For NaN == and == return false always even NaN == NaN is false, to check if a value is NaN use isNaN(value)
//For undefined it evaluates to false in boolean operations. Always use === when comparing to undefined.
//If we use === the results are more what you would expect , cause there is no type coercion
console.log( null === false ); // false
console.log( 0 === false ); // false
console.log( "" === false ); // false
console.log( false === false ); // true
console.log( NaN === false ); // false
console.log( undefined === false ); // false
Please Whitelist JSFiddle in your content blocker.
Help keep JSFiddle free for always by one of two ways:
Whitelist JSFiddle in your content blocker (two clicks)
Go PRO and get access to additional PRO features →
Join the 4+ million users, and keep the JSFiddle dream alive.
Ad-free
All ads in the editor and listing pages are turned completely off.
Use pre-released features
You get to try and use features (like the Palette Color Generator) months before everyone else.
Fiddle collections
Sort and categorize your Fiddles into multiple collections.
Private collections and fiddles
You can make as many Private Fiddles, and Private Collections as you wish!
Console
Debug your Fiddle with a minimal built-in JavaScript console.