Change class of an element with JS

[Renno]

Hi,

I understood that I can change the style of elements one by one by manipulating the *style property*. This is OK, but I was wondering if there is a way to change classes the same way we can do in modern JS. For example:

let myBigBox = document.getElementById("myBigBox");
myBox.classList.add("bigBox");
mybox.classList.remove("blue");
let myLittleRedBox = document.getElementById("myLittleBox");
myLittleRedBox.classList.add("littleBox");
myLittleRedBox.classList.add("red");

I tried to use the *classList* property, but I keep getting the classic *undefined*. Let me know if this is possible. Thanks!

[JeCom]

Maybe this will work?

myLittleRedBox.className += " littleBox red";

[JonFitbit]

Unfortunately there's no way to dynamically change an element's class name right now.

[Renno]

This might work if your case is very simple. There are a few problems with this implementation:

1) You will concatenate more than one class if your event happens more than once;

2) To remove is a pain; You probably have to use something like

myLittleRedBox.className = myLittleRedBox.replace('your-unique-class', '');
// or use regex, splice, etc...

Thanks for the suggestion, though. I appreciate it.

[JeCom]

You can retrieve the separate classes by string manipulation. It's not very "clean" but it's possible.

Here are the steps you can take (untested, by the top of my head):

var classesAsString = myLittleRedBox.className;
// maybe remove all spaces beforehand with eg this replace solution
// put the classNames in an array by splitting on the comma
var classesSplit = classesAsString.split(","); 
// remove class by splicing the classname you want to remove
var indexOfClassToRemove = classesSplit .indexOf("classToRemove");
if (index > -1) {  classesSplit.splice(index, 1);
}
// build up the new class value by using join
myLittleRedBox.className = classesSplit.join();

[SunsetRunner]

Fundamental problem is that neither className or classList are exposed in JS, as JonFitbit already said.

Both give undefined, so nothing is going to work.

This is a real pain - the idea of using SVG for the UI is cool, but not if basic manipulation features are missing.

[jeremiahlee]

Not being able to change a className on an element is a huge pain in the arse and a tragic hole in the SDK capabilities.

[SunsetRunner]

class is now supported in SDK 4, and it works great - you can easily change  colours and visibility just by changing the class of the SVG element with the appropriate CSS.

Nice 🙂

[malfandre]

Any update on this. Is this possible yet?

[Gondwana]

https://dev.fitbit.com/blog/2019-12-19-announcing-fitbit-os-sdk-4.1/