Message from JavaScript discussions

September 2017

— Currently my iterator only skips undefined regardless, which is bad


So I need to be able to tell this:

var arr = [];
arr[50] = "hello world";

From this:
var arr = [];
arr[49] = undefined;
arr[50] = "hello world";

— Currently I don't know of a way to tell these two arrays apart

— Other than using a loop or other discrete builtin

— Here is how I currently do it:

Message permanent page

— It does not tell those two arrays apart and correctly iterate the assigned index 49

— The problem is hasOwnProperty is slow on objects, but what about Arrays? Maybe index in arr is faster

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— Oki guys, a question for you without looking up the reason.

null > 0 //false
null === 0 //false
null >= 0 //true


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— Coercion, null coerces to false and false coerces to 0, that gives answer to 1 and 3

— === checks value as well as type

— Null == 0 is false as well.

— null == 0 but typeof null != typeof 0,

Edit: null != 0