三十一.ID查询

<div id="app">
        app
        <div class="one">one1</div>
        <div class="one">one1</div>
        <div class="one">one1</div>
    </div>

  var app = document.getElementById("app");
        console.log(app);
        // NodeList
        var all = document.querySelectorAll(".one");
        console.log(all)