add to classlist javascript

 document.getElementById("myDIV").classList.add("mystyle"); 

classList.item(index); // Returns the item in the list by its index, or undefined if index is greater than or equal to the list's length
classList.contains(token); // Returns true if the list contains the given token, otherwise false.
classList.add(token1[, ...tokenN]); // Adds the specified token(s) to the list.
classList.remove(token1[, ...tokenN]); // Removes the specified token(s) from the list.
classList.replace(oldToken, newToken); // Replaces token with newToken.
classList.supports(token); // Returns true if a given token is in the associated attribute's supported tokens.
classList.toggle(token[, force]); // Removes token from the list if it exists, or adds token to the list if it doesn't. Returns a boolean indicating whether token is in the list after the operation.
classList.entries(); // Returns an iterator, allowing you to go through all key/value pairs contained in this object.
classList.forEach(callback[ ,thisArg]); // Executes a provided callback function once per DOMTokenList element.
classList.keys(); // Returns an iterator, allowing you to go through all keys of the key/value pairs contained in this object.
classList.values(); // Returns an iterator, allowing you to go through all values of the key/value pairs contained in this object.

Add multiple classes to a <div> element:
document.getElementById("myDIV").classList.add("mystyle", "anotherClass", "thirdClass");

Remove a class from a <div> element:
document.getElementById("myDIV").classList.remove("mystyle");

Remove multiple classes from a <div> element:
document.getElementById("myDIV").classList.remove("mystyle", "anotherClass", "thirdClass");

Toggle between two classes for a <div> element:
document.getElementById("myDIV").classList.toggle("newClassName");

Find out if an element has a "mystyle" class:
document.getElementById("myDIV").classList.contains("mystyle");

//get array of class names in Javascript
var classesArray = document.getElementById('myElementID').className.split(/\s+/);