+ 22

What is the diffrence (in examples) between undefined, null, NaN ?

Difrences: Undefined Null NaN

24th Apr 2019, 6:33 PM
SĹ‚awek J.
10 Answers
+ 15
In general things are never null unless you manually set them to null, but many things are undefined by default. Some interesting examples: > typeof null "object" > typeof undefined "undefined" > typeof NaN "number" // even though it's Not a Number :D > NaN == NaN false > NaN != NaN true function foo() { } > foo() undefined var foo; > foo undefined > null == undefined true > null === undefined false > [].find(x => true); undefined > [].reduce(() => 0); Uncaught TypeError > 1/0 Infinity > 0/0 NaN > Number(null) 0 > Number(undefined) NaN
24th Apr 2019, 7:58 PM
Schindlabua
Schindlabua - avatar
+ 13
Undefined means that something has no definded value. Null is the specific value to express nothing. NaN means not a number an is the value that is returned from ilegal mathimatical expressions.
24th Apr 2019, 7:43 PM
Dragonxiv
Dragonxiv - avatar
+ 10
Undefined mean when you didn't declare a variable but you call in this variable. Null mean when you create a object or create string variable but you didn't inialize the value.
25th Apr 2019, 4:14 PM
Nasir❤
Nasir❤ - avatar
+ 8
Undefined = a variable was not defined Null = a variable has nothing(0) NaN = Not a Number e.g: console.log('abc' * 3) will return a error NaN
25th Apr 2019, 4:44 AM
Darcy Dev
Darcy Dev - avatar
+ 5
I'm not aware of anything that returns null, unless you do it yourself. var foo = null; > foo null function foo() { return null; } > foo() null That means if you the want to explicitly communicate that some value is missing, you want to use null because so many things are undefined. For example, if you have var foo; And you later use that variable and get an error because "something something undefined", that error can mean so many different things (typo, forgot to pass a parameter to a function, forgot to set a property of an object, and a hundred other things). if you have var foo = null; and get an error because "something something null", you know that somehow somewhere you set that variable to null yourself. It helps a lot when debugging. But all in all the differences are pretty minor.
25th Apr 2019, 9:30 AM
Schindlabua
Schindlabua - avatar
+ 5
If on a prompt call the user clicks cancel, null is returned.
25th Apr 2019, 9:44 AM
HonFu
HonFu - avatar
+ 4
Oof, why would they even do that.
25th Apr 2019, 9:47 AM
Schindlabua
Schindlabua - avatar
+ 2
Give them a button, eventually they'll use it. ;)
25th Apr 2019, 12:07 PM
HonFu
HonFu - avatar
+ 2
I wonder, what type of number is NaN
25th Apr 2019, 9:23 PM
\•/
\•/ - avatar
+ 2
To better understand "Undefined": https://youtu.be/Bv_5Zv5c-Ts?t=2793
29th Apr 2019, 10:46 PM
codeKameleon
codeKameleon - avatar