JavaScript Fundamentals: Checking for null and undefined

The primitive values null and undefined have a distinct difference that should be used. But how to you tell the difference between a null value, an undefined value and other falsey values? We will address it in this tutorial.

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Tutorials referred to in this video:

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[edcoughlan]

Null = intentional absence of value; undefined = unintentional is a very good distinction. Thanks for clearing that up!

[ashamula]

var val1, val2 = {}, val3 = ' ', val4 = 0; val5 = [];
if(val1 == null && val3.length === 0 && val5.length === 0 ) { console.log('value is absent -- val1, val 3 and val 5') };
if(Object.keys(val2).length === 0) { console.log('value is absent -- val2') };
if(val4 === 0) { console.log('value is absent -- val4') };

if the value is an empty string or empty array we can use length to find and if the object is an empty object we can use the Object inbuild method. Hope this covers all the scenarios

[fattah]

This explains everything about undefined. Thanks a lot for clear explanation ^_^

[Petar_Ral]

or you could do: if(value != 0) then check for null/undefined.

[GregoryGilelach]

Great tutorial! Could you make another one about !! operator?

[artistunknown]

hey so like what ap do i use to write javascript ? i was using my notes on my macbook

[luizmeier]

Checking if a variable is = [ ] is also important (mainly when working with APIs).

var something = [ ] ;

if (something === undefined || something.length == 0) { }