Why it isn't work?

Question

Why it isn't work?

I want to changing properties with java script but i got error

https://code.sololearn.com/WMw5w08zPAL4/?ref=app

Answer 1

getElementsByClassName doesn't return an array btw.

Answer 2

"The getElementsByClassName method of Document interface returns an array-like object of all child elements which have all of the given class name(s)."
~MDN

The returned HTMLCollection doesn't have a style property.

As if you want to access nth element you can access it using index n -1

To access first matching element use index 0

//Correct code :

document
.getElementsByClassName("test")[0]
.style.backgroundColor = "blue" ;

See how [0] used after ("test")

https://developer.mozilla.org/en-US/docs/Web/API/Document/getElementsByClassName