DEV Community

Cover image for NUll vs Undefined

NUll vs Undefined

GiandoDev on April 19, 2020

In JavaScript we have seven primitives: string number boolean null undefined symbol bigInit We often think that null and undefined are the sam...
Read full post
Collapse
 
nicom64 profile image
nicom64 • • Edited

Hi,
You know you can find the type of a value with the typeof command :

typeof 'string'      // --> "string"
typeof 10            // --> "number"
typeof true          // --> "boolean"
typeof undefined     // --> "undefined"

Just remember : the type of the value null should be normally null, but it's not !

typeof null          // --> "object"

It's a very interesting story about a little bug insidiously introduced at the very beginning of the JS implementation (a tiny neglected of an if statement fot this type !) described here, and will never be fixed (too late !).

However, this tale highly helps me remember the case !

Collapse
 
fennecdjay profile image
Jérémie Astor •

In Gwion, I actually implemented @null type (the type of null) as inheriting from Object, as it means absence of an object. It's true this way needs a few special rules to match, say, function pointers but it works well this way.