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element.classList returns an array of classes, its my understanding .includes() is used with arrays, so I don't understand why this wont work, I know I can use .contains() with classList but I'm curious as to why .includes() doesn't work.
both are arrays, if I typed this for example it wont work
var li=document.createElement('li'); li.classList.add('main-nav'); li.classList.includes('main-nav'); but this will
var ary=['a','b','c']; ary.includes('a'); 
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toggle() The toggle() button is used for toggling classes to the element. It means adding a new class or removing the existing classes.
classList returns an array of classes, its my understanding .
classList is a read-only property that returns a live DOMTokenList collection of the class attributes of the element. This can then be used to manipulate the class list. Using classList is a convenient alternative to accessing an element's list of classes as a space-delimited string via element. className .
classList property The classList property has add() and remove() methods that allow passing multiple classes as arguments. Let's say we have a button with id value of button . To add multiple classes, you'll need to pass each class as a separate parameter to the add method.
Element.classList is a DOMTokenList object, though it prints an array-like in console. But if you try on Firefox, it'd return DOMTokenList["main-nav"]
And, includes is a method of Array instead of DOMTokenList.
Which is why it's expected to encounter li.classList.includes is not a function in your case.
You can use ES2015 spread operator to cast it to be an array.
[...li.classList].includes('main-nav') Or alternatively, you can use DOMTokenList.contains method.
li.classList.contains('main-nav') Why is it declared as includes instead of has or contains? (thanks to @akinuri)
Quoting from the proposal
The web has classes like DOMStringList and DOMTokenList which are array-like, and have methods named contains with the same semantics as our includes. Unfortunately, meshing with those is not web-compatible.
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