Js选择器

JS选择器常用的有getElementById()getElementsByClassName()getElementsByName()getElementsByTagName()querySelector()querySelectorAll()

getElementById

通过id来定位,返回对指定id的第一个对象的引用,返回类型为HTMLDivElement

<div id="t1">T1</div>

<script type="text/javascript">
    var t1 = document.getElementById("t1");
    console.log(t1); // <div id="t1">D1</div>
    console.log(Object.prototype.toString.call(t1)); // [object HTMLDivElement]
</script>

getElementsByClassName

通过class属性来定位,返回文档中指定class属性值的元素的引用,返回类型为HTMLCollection

<div class="t2">D2</div>
<div class="t2">D3</div>

<script type="text/javascript">
    var t2List = document.getElementsByClassName("t2");
    console.log(t2List); // HTMLCollection(2) [div.t2, div.t2]
    // 使用for循环遍历
    for(let i=0,n=t2List.length;i<n;++i) console.log(t2List[i]);
    // HTMLCollection的prototype中没有forEach方法,遍历需要使用Array的prototype中forEach通过call绑定对象实例并传参
    Array.prototype.forEach.call(t2List,v => console.log(v) ); 
    // HTMLCollection的prototype中没有map方法,也需要使用Array的prototype中forEach通过call绑定对象实例并传参
    Array.prototype.map.call(t2List,v => console.log(v) ); 
</script>

getElementsByName

通过name属性来定位,返回文档中指定name属性值的元素的引用,返回类型为NodeList

<div name="t3">D4</div>
<div name="t3">D5</div>

<script type="text/javascript">
    var t3List = document.getElementsByName("t3");
    console.log(t3List); // NodeList(2) [div, div]
    // 可直接使用forEach进行遍历
    t3List.forEach( v => console.log(v) ); 
    // NodeList的prototype中没有map方法,使用map的场景也需要借助Array的prototype中map通过call绑定对象实例并传参
    Array.prototype.map.call(t3List,v => console.log(v) ); 
</script>

getElementsByTagName

通过标签的名字来定位,返回文档中指定标签的元素的引用,返回类型为HTMLCollection

<p class="t4">P6</p>
<p class="t4">P7</p>

<script type="text/javascript">
    var t4List = document.getElementsByTagName("p");
    console.log(t4List); // HTMLCollection(2) [p, p]
    Array.prototype.forEach.call(t4List, function(v){console.log(v);}); 
    Array.prototype.map.call(t4List,function(v){console.log(v);} ); 
</script>

querySelector

通过CSS选择器来定位,返回文档中匹配指定CSS选择器的第一个元素的引用,返回类型为HTMLDivElement

<div>
    <div class="t5">D8</div>
</div>

<script type="text/javascript">
    var t5 = document.querySelector("div .t5");
    console.log(t5); // <div class="t5">D8</div>
    console.log(Object.prototype.toString.call(t5)); // [object HTMLDivElement]
</script>

querySelectorAll

通过CSS选择器来定位,返回文档中匹配指定CSS选择器的所有元素的引用,返回类型为NodeList

<div>
    <div id="t6">D9</div>
    <div>D10</div>
    <div>D11</div>
</div>

<script type="text/javascript">
     var t6List = document.querySelectorAll("#t6 ~ div");
    console.log(t6List); // NodeList(2)[div, div]
    t6List.forEach(function(v){console.log(v);}); 
    Array.prototype.map.call(t6List,function(v){console.log(v);} ); 
</script>

代码示例

<!DOCTYPE html>
<html>
<head>
    <title>Js选择器</title>
    <meta charset="utf-8">
</head>
<body>

    <div id="t1">D1</div>

    <div class="t2">D2</div>
    <div class="t2">D3</div>

    <div name="t3">D4</div>
    <div name="t3">D5</div>

    <p class="t4">P6</p>
    <p class="t4">P7</p>

    <div>
        <div class="t5">D8</div>
    </div>

    <div>
        <div id="t6">D9</div>
        <div>D10</div>
        <div>D11</div>
    </div>

</body>
<script type="text/javascript">
    var t1 = document.getElementById("t1");
    console.log(t1); // <div id="t1">D1</div>
    console.log(Object.prototype.toString.call(t1)); // [object HTMLDivElement]
    console.log("");

    var t2List = document.getElementsByClassName("t2");
    console.log(t2List); // HTMLCollection(2) [div.t2, div.t2]
    // 使用for循环遍历
    for(let i=0,n=t2List.length;i<n;++i) console.log(t2List[i]);
    // HTMLCollection的prototype中没有forEach方法,遍历需要使用Array的prototype中forEach通过call绑定对象实例并传参
    Array.prototype.forEach.call(t2List,v => console.log(v) ); 
    // HTMLCollection的prototype中没有map方法,也需要使用Array的prototype中forEach通过call绑定对象实例并传参
    Array.prototype.map.call(t2List,v => console.log(v) ); 
    console.log("");

    var t3List = document.getElementsByName("t3");
    console.log(t3List); // NodeList(2) [div, div]
    // 可直接使用forEach进行遍历
    t3List.forEach( v => console.log(v) ); 
    // NodeList的prototype中没有map方法,使用map的场景也需要借助Array的prototype中map通过call绑定对象实例并传参
    Array.prototype.map.call(t3List,v => console.log(v) ); 
    console.log("");

    var t4List = document.getElementsByTagName("p");
    console.log(t4List); // HTMLCollection(2) [p, p]
    Array.prototype.forEach.call(t4List, function(v){console.log(v);}); 
    Array.prototype.map.call(t4List,function(v){console.log(v);} ); 
    console.log("");

    var t5 = document.querySelector("div > .t5");
    console.log(t5); // <div class="t5">D8</div>
    console.log(Object.prototype.toString.call(t5)); // [object HTMLDivElement]
    console.log("");

    var t6List = document.querySelectorAll("#t6 ~ div");
    console.log(t6List); // NodeList(2) [div, div]
    t6List.forEach(function(v){console.log(v);}); 
    Array.prototype.map.call(t6List,function(v){console.log(v);} ); 
    console.log("");
</script>
</html>

每日一题

https://github.com/WindrunnerMax/EveryDay

参考

数组的遍历 https://github.com/WindrunnerMax/EveryDay/blob/master/JavaScript/Js%E9%81%8D%E5%8E%86%E6%95%B0%E7%BB%84%E6%80%BB%E7%BB%93.md ES6箭头函数 https://github.com/WindrunnerMax/EveryDay/blob/master/JavaScript/ES6%E6%96%B0%E7%89%B9%E6%80%A7.md 原型与原型链 https://github.com/WindrunnerMax/EveryDay/blob/master/JavaScript/%E5%8E%9F%E5%9E%8B%E4%B8%8E%E5%8E%9F%E5%9E%8B%E9%93%BE.md CSS选择器 https://github.com/WindrunnerMax/EveryDay/blob/master/CSS/CSS%E9%80%89%E6%8B%A9%E5%99%A8.md