通过在 Javascript 中单击外部来关闭下拉菜单（教程说明）

我尝试通过以下方式使用 Javascript 实现打开和关闭下拉菜单的方法this https://www.w3schools.com/howto/howto_js_dropdown.aspw3schools.com 上的教程。虽然“显示”下拉菜单的功能有效，但关闭下拉菜单的功能却不起作用。此外，这段代码旁边没有任何解释来解释为什么它should工作，使得调试变得困难。

/* When the user clicks on the button, 
toggle between hiding and showing the dropdown content */
function myFunction() {
    document.getElementById("myDropdown").classList.toggle("show");
}

// Close the dropdown menu if the user clicks outside of it
window.onclick = function(event) {
  if (!event.target.matches('.dropbtn')) {

    var dropdowns = document.getElementsByClassName("dropdown-content");
    var i;
    for (i = 0; i < dropdowns.length; i++) {
      var openDropdown = dropdowns[i];
      if (openDropdown.classList.contains('show')) {
        openDropdown.classList.remove('show');
      }
    }
  }
}

因此，我的问题是

1）是否有教程中的代码should用于关闭下拉菜单的目的。 （已回答）

2）为了让我自己和未来遇到相同教程和问题的新手清楚起见，有人可以澄清这应该如何/为什么起作用吗？ （未答复）

编辑（我的尝试）：

HTML:

<div class="sharedown">     
    <p onclick="shareVis()" class="sharebtn">&nbsp Share</p>
    <div id="mySharedown" class="sharedown-content">
        <a href="#">Self</a>
        <p>User</p><input type="text" name="user-name" placeholder="Share to">
        <a href="#">Community</a>
    </div> 
</div>

JS:

function shareVis() {
    document.getElementById("mySharedown").className = "show";
}

window.onclick = function(event) {
    if (!event.target.matches('sharebtn')) {

        var sharedowns = document.getElementsByClassName("sharedown-content");
        var i;
        for (i = 0; i < sharedowns.length; i++) {
            var openSharedown = sharedowns[i];
            if (openSharedown.classList.contains('show')) {
                openSharedown.classList.remove('show');
            }
        }
    }   
}

CSS:

/* Share dropdown menu */

p.sharebtn {

    color: darkgrey;
    font-family:calibri;
    padding: 0px;
    margin: 0px;
    font-size: 12;
    border: none;
    cursor: pointer;
    display:    inline; 
}

/* Dropdown button on hover & focus */
p.sharebtn:hover, p.sharebtn:focus {
    color: grey;

}

/* The container <div> - needed to position the dropdown content */

.sharedown {
    position: relative;
    display:    inline-block;   

}

/* Dropdown Content (Hidden by Default) */
.sharedown-content {
    display: none;
    position: absolute;
    background-color:   #f1f1f1;
    min-width:  100px;
    box-shadow: 0 2px 4px 1px #C4E3F5;
    z-index:1; /* place dropdown infront of everything else*/
}

.sharedown-content a { 
color: black;
padding: 5px 5px;
text-decoration: none;
display: block;
}

/* Show the dropdown menu (use JS to add this class to the .dropdown-
content container when the user clicks on the dropdown button) */

.show {display: block;
    position: absolute;
    background-color:   #f1f1f1;
    min-width:  100px;
    box-shadow: 0 2px 4px 1px #C4E3F5;
    opacity: 1;
    z-index:1;}

问题在于shareVis功能。这里

document.getElementById("mySharedown").className = "show";

你正在替换#mySharedown类名至show。然后在window.onclick

var sharedowns = document.getElementsByClassName("sharedown-content");

你没有得到任何sharedowns因为您已经将类名替换为show.

document.getElementById("mySharedown").classList.add("show");

或将类名替换为sharedown-content show

document.getElementById("mySharedown").className = "sharedown-content show";

工作解决方案如下：

function shareVis() {
    //document.getElementById("mySharedown").className = "sharedown-content show";
    document.getElementById("mySharedown").classList.add("show");
}

window.onclick = function(event) {
    if (!event.target.matches('.sharebtn')) {

        var sharedowns = document.getElementsByClassName("sharedown-content");
        var i;
        for (i = 0; i < sharedowns.length; i++) {
            var openSharedown = sharedowns[i];
            if (openSharedown.classList.contains('show')) {
                openSharedown.classList.remove('show');
            }
        }
    }
}

document.getElementById("mySharedown").addEventListener('click',function(event){
    event.stopPropagation();
});

#mySharedown{
  display: none;
  border: 1px solid black;
}

#mySharedown.show {
  display: block;
}

<div class="sharedown">     
    <p onclick="shareVis()" class="sharebtn">&nbsp Share</p>
    <div id="mySharedown" class="sharedown-content">
        <a href="#">Self</a>
        <p>User</p><input type="text" name="user-name" placeholder="Share to">
        <a href="#">Community</a>
    </div> 
</div>

Update

为了防止第二次点击#mySharedown躲起来#mySharedown，你应该添加另一个click活动为#mySharedown并防止它冒泡，就像这样

document.getElementById("mySharedown").addEventListener('click',function(event){
    event.stopPropagation();
});

更新包含在工作解决方案中