1、Add class name:
document.getElementById("myDiv").classList.add("myStyle");
2、Delete class name:
document.getElelmentById("myDiv").classList.remove("myStyle")
3、Check whether there is any CSS fatigue:
myDiv.classList.contains("myCssStyle")
//return true or false
Note: when we add multiple class names, we write them side-by-side and separate them with commas.