var list = document.getElementsByClassName("class1 class2");
var list = document.querySelectorAll(".class1.class2");document.getElementsByClassName('class1 class2')var list = document.querySelectorAll(".class1.class2");
//Class1 AND Class2
var list = document.querySelectorAll(".class1,class2");
//Class1 OR Class2document.querySelectorAll('.a,.b')
var elems = document.getElementsByClassName("class1 class2 class3");