Adds a class attribute to the element using a given string.
Calling myElement.class() without an argument returns a string with its current classes.
示例
语法
class(class)
class()
参数
class
String: class to add.
返回值
String: element's classes, if any.
Notice any errors or typos? Please let us know. Please feel free to edit src/dom/p5.Element.js and open a pull request!