https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelectorAllcode
https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelectorblog
https://developer.mozilla.org/en-US/docs/Web/API/Document/getElementById繼承
getElementById 僅支持 id 選擇器, 返回 An Element object接口
querySelector 支持各類選擇器, 返回匹配的第一個 An HTMLElement objectelement
https://developer.mozilla.org/en-US/docs/Web/API/Elementget
https://developer.mozilla.org/en-US/docs/Web/API/HTMLElementio
document.getElementById("demo"); <section id="demo"> </section> document.querySelector("#demo") <section id="demo"> </section> document.querySelectorAll("#demo") NodeList [section#demo]0: section#demolength: 1__proto__: NodeList document.getElementById("demo") === document.querySelector("#demo") true document.getElementById("demo") == document.querySelector("#demo") true typeof document.getElementById("demo") "object" typeof document.querySelector("#demo") "object"