JavaScript-获取DOM元素

  • 在 JavaScript 中 HTML 标签也称之为 DOM 元素
  • 使用 document 的时候前面不用加 window

例如下面的一个小示例

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
    <script>
        var num = 666;
        console.log(window.num);
        console.log(num);
    </script>
</head>
<body>

</body>
</html>

image-20210804161029270

document 同理可证

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
    <script>
        console.log(window.document);
        console.log(document);
    </script>
</head>
<body>

</body>
</html>

image-20210804161043192

通过 id 获取指定元素

  • 由于 id 不可以重复，所以找到了就会将找到的标签包装成一个对象返回给我们，找不到就返回 Null
  • 注意点：DOM 操作返回的是一个对象，这个对象是宿主类型对象 (浏览器提供的对象)
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div class="father">
    <form>
        <input type="text" name="username"/>
        <input type="password" name="password"/>
    </form>
</div>
<div class="father" id="box">我是div</div>

<script>
    let oDiv = document.getElementById("box");
    console.log(oDiv);
    console.log(typeof oDiv);
</script>
</body>
</html>

image-20210804162511002

通过 class 名称获取

  • 由于 class 可以重复，所以找到了就返回一个存储了标签对象的数组，找不到就返回一个空数组
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div class="father">
    <form>
        <input type="text" name="username"/>
        <input type="password" name="password"/>
    </form>
</div>
<div class="father" id="box">我是div</div>

<script>
    let oDivs = document.getElementsByClassName("father");
    console.log(oDivs);
</script>
</body>
</html>

image-20210804163021818

通过 name 名称获取

  • 由于 name 可以重复，所以找到了就返回一个存储了标签对象的数组，找不到就返回一个空数组
  • 注意点：getElementsByName 在不同的浏览器中工作的方式不同。在 IE 和 Opera 中，getElementsByName() 方法还会返回那些 id 为指定值的元素
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div class="father">
    <form>
        <input type="text" name="test"/>
        <input type="password" name="test"/>
    </form>
</div>
<div class="father" id="box">我是div</div>

<script>
    let oDivs = document.getElementsByName("test");
    console.log(oDivs);
</script>
</body>
</html>

image-20210804163640108

通过标签名称获取

  • 由于标签名称可以重复，所以找到了就返回一个存储了标签对象的数组，找不到就返回一个空数组
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div class="father">
    <form>
        <input type="text" name="test"/>
        <input type="password" name="test"/>
    </form>
</div>
<div class="father" id="box">我是div</div>

<script>
    let oDivs = document.getElementsByTagName("div");
    console.log(oDivs);
</script>
</body>
</html>

image-20210804164200470

通过选择器获取

  • querySelector 只会返回根据指定选择器找到的第一个元素
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div class="father">
    <form>
        <input type="text" name="test"/>
        <input type="password" name="test"/>
    </form>
</div>
<div class="father" id="box">我是div</div>

<script>
    let oDivOne = document.querySelector("#box");
    let oDivTwo = document.querySelector(".father");
    let oDivThree = document.querySelector("div>form");

    console.log(oDivOne);
    console.log(oDivTwo);
    console.log(oDivThree);
</script>
</body>
</html>

image-20210804164423018

  • querySelectorAll 会返回指定选择器找到的所有元素
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div class="father">
    <form>
        <input type="text" name="test"/>
        <input type="password" name="test"/>
    </form>
</div>
<div class="father" id="box">我是div</div>

<script>
    let oDivs = document.querySelectorAll(".father");
    console.log(oDivs);
</script>
</body>
</html>

image-20210804164743443

获取指定元素所有的子元素

  • children 属性获取到的是指定元素中所有的子元素
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let oDiv = document.querySelector("div");

    console.log(oDiv.children);
</script>
</body>
</html>

image-20210804190802798

  • childNodes 属性获取到的是指定元素中所有的节点
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let oDiv = document.querySelector("div");

    console.log(oDiv.childNodes);
</script>
</body>
</html>

image-20210804190825417

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let oDiv = document.querySelector("div");

    for (let node of oDiv.childNodes) {
        // console.log(node.nodeType);
        if (node.nodeType === Node.ELEMENT_NODE) {
            console.log(node);
        }
    }
</script>
</body>
</html>

什么是节点

  • DOM 对象(document)，这个对象以树的形式保存了界面上所有的内容
  • HTML 页面每一部分都是由节点(标签(元素)、文本、属性)

获取指定节点中的第一个子节点

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let oDiv = document.querySelector("div");
    console.log(oDiv.firstChild);
</script>
</body>
</html>

获取指定元素中的第一个子元素

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let oDiv = document.querySelector("div");
    console.log(oDiv.firstElementChild);
</script>
</body>
</html>

获取指定节点中最后一个子节点

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let oDiv = document.querySelector("div");
    console.log(oDiv.lastChild);
</script>
</body>
</html>

获取指定元素中最后一个子元素

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let oDiv = document.querySelector("div");
    console.log(oDiv.lastElementChild);
</script>
</body>
</html>

通过子元素获取父元素/父节点

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let item = document.querySelector(".item");
    console.log(item.parentElement);
    console.log(item.parentNode);

    let parentEle = item.parentElement || item.parentNode;
    console.log(parentEle);
</script>
</body>
</html>

获取相邻上一个节点

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let item = document.querySelector(".item");
    console.log(item.previousSibling);
</script>
</body>
</html>

获取相邻上一个元素

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let item = document.querySelector(".item");
    console.log(item.previousElementSibling);
</script>
</body>
</html>

获取相邻下一个节点

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let item = document.querySelector(".item");
    console.log(item.nextSibling);
</script>
</body>
</html>

获取相邻下一个元素

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
</head>
<body>
<div>
    <h1>1</h1>
    <h2>2</h2>
    <p class="item">3</p>
    <p>4</p>
    <span>5</span>
</div>

<script>
    let item = document.querySelector(".item");
    console.log(item.nextElementSibling);
</script>
</body>
</html>

End

posted @ 2021-08-04 16:49  BNTang  阅读(171)  评论(0)  编辑  收藏  举报