DOM选择器；innerHTML和outerHTML区别

DOM选择器

    document.getElementById//通过id
    document.getElementsByClassName//通过类名
    document.getElementsByTagName//通过标签
    document.querySelector//常用，选取一个
    document.querySelectorAll//常用，选取多个

innerHTML和outerHTML区别

    let demo = document.getElementById('demo')
    console.log(demo.innerHTML);//  Hello
    console.log(demo.outerHTML); //<div id="demo">  Hello  </div>   包含自身的标签