Javascript check for undefined quotes

[SilverDash]

// In Game_Eventtypeof this.page() === undefined // doesn't worktypeof this.page() === 'undefined' // works// also requires quotes around the undefined.(typeof Silv.Minimap.POI[$gameMap._mapId] === 'undefined')// But then in DataManager.onLoad:if (data && data.note !== undefined) // <<<< no quotes! huh?Erm... huh? When to quote undefined?

 

[Iavra]

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/typeof

The typeof operator returns a string indicating the type of the unevaluated operand.

undefined itself is an immutable object residing in the public scope, while 'undefined' is the string representation of its type.

 

[Mellye]

The typeof operator always returns a string. So if you're using it to check the type of something, you need to compare it to 'undefined' (with quotemarks, as it is a string).

When you compare something directly to undefined (without quotemarks, and without using typeof), you're actually just comparing it to a global variable that doesn't exist - one that is undefined. So two undefined things comparing to each other will return true.

 

[DarknessFalls]

use typeof instead or instanceof. If you know how to pull in third party libraries, use lodashes isUndefined function

 

[SilverDash]

Oh I see the typeof is what changes everything. Thanks all.