document getElements series

1.getElementsByName() 方法
https://www.w3school.com.cn/jsref/met_doc_getelementsbyname.asp

2.getElementById () method
https://www.w3school.com.cn/jsref/met_doc_getelementbyid.asp

3.document.getElementByclassName（）方法
https://blog.csdn.net/boat_sea/article/details/80142875

4.querySelector() 方法
document.querySelector("h2, h3").style.backgroundColor = "red";
https://www.runoob.com/jsref/met-document-queryselector.html

difference document.querySelector and document.getElementByClassName of
https://blog.csdn.net/u013718730/article/details/90474272

Detailed document.getElementById difference and document.querySelector of
https://blog.csdn.net/m0_37793545/article/details/79193254

document.getElementById / Name / TagName small differences return value
https://www.jianshu.com/p/151c5a283c3e