Introducing the offset, client, and scroll family properties of JavaScript-JS Tutorial-php.cn

偏移量(offset dimension)是javascript中的一个重要的概念。涉及到偏移量的主要是offsetLeft、offsetTop、offsetHeight、offsetWidth这四个属性。当然，还有一个偏移参照——定位父级offsetParent。本文将详细介绍该部分内容

定位父级

在理解偏移大小之前，首先要理解offsetParent。人们并没有把offsetParent翻译为偏移父级，而是翻译成定位父级，很大原因是offsetParent与定位有关

定位父级offsetParent的定义是：与当前元素最近的经过定位(position不等于static)的父级元素，主要分为下列几种情况

元素自身有fixed定位，offsetParent的结果为null

当元素自身有固定定位时，我们知道固定定位的元素相对于视口进行定位，此时没有定位父级，offsetParent的结果为null

　[注意]firefox浏览器有兼容性问题

<p id="test" style="position:fixed"></p>    <script>
   var test = document.getElementById('test');   //firefox并没有考虑固定定位的问题，返回<body>，其他浏览器都返回null
   console.log(test.offsetParent);</script>复制代码

Copy after login

元素自身无fixed定位，且父元素都没有设置定位，offsetParent的结果为body

1 2	`<p id="test"></p> <script>` `var` `test = document.getElementById('test'); console.log(test.offsetParent);//<body></script>复制代码`

Copy after login

元素自身无fixed定位，且父级元素存在经过定位的元素，offsetParent的结果为离自身元素最近的经过定位的父级元素

<p id="grandfather" style="position: relative;">
    <p id="father" >
        <p id="test"></p>
    </p></p><script type="text/javascript">
    var test = document.getElementById('test');    // 距离该子元素最近的进行过定位的父元素,如果其父元素不存在定位则offsetParent为:body元素;
    console.log(test.offsetParent);</script>复制代码

Copy after login

<body>元素的offsetParent是null

1	`console.log(document.body.offsetParent);//null复制代码`

Copy after login

偏移量

偏移量共包括了offsetHeight、offsetWidth、offsetLeft、offsetTop这四个属性

offsetWidth

offsetWidth表示元素在水平方向上占用的空间大小，无单位(以像素px计)

1 2	`offsetWidth = border-left-width + padding-left + width + padding-right + border-right-width;` `复制代码`

Copy after login

offsetHeight

　　offsetHeight表示元素在垂直方向上占用的空间大小，无单位(以像素px计)

1	`offsetHeight = border-top-width + padding-top + height + padding-bottom + border-bottom-width复制代码`

Copy after login

测试：

<!DOCTYPE html><html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
        <style>
            #box {             width: 200px;              height: 150px;             background-color: red;             padding: 10px;             border: 5px solid #ddd;              margin: 10px;
            }       </style>
    </head>
    <body>
        <p id="box" style="width: 100px;height: 100px;"></p>
        <script>
            var box = document.getElementById('box');            //offsetHeight = 内容高 + 上下内边距 + 边框
            console.log(box.offsetWidth,box.offsetHeight);          console.log(box.style.width, box.style.height);            // 可以设置大小
            // box.style.width = 500 + 'px';
            // 不可以设置大小
            box.offsetWidth = 100 + 'px';       </script>
 
    </body></html>复制代码

Copy after login

注意：如果想修改盒子的大小，请使用xxx.style.width进行设置。offsetWidth和offsetHeight是只读属性

offsetTop

　　offsetTop表示元素的上外边框至offsetParent元素的上内边框之间的像素距离

offsetLeft

　　offsetLeft表示元素的左外边框至offsetParent元素的左内边框之间的像素距离

测试:

<!DOCTYPE html><html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <style type="text/css">
            *{              padding: 0;                margin: 0;
            }           #father{                width: 400px;              height: 400px;             background-color: red;             /* position: relative; */
                margin: 40px;
            }           #son {             width: 200px;              height: 100px;             background-color: green;               padding: 10px;             border: 5px solid #DA70D6;               margin-left: 20px;
            }       </style>
    </head>
    <body>
        <p id="father">
            <p id="son"></p>
        </p>
        <script type="text/javascript">
            var box = document.getElementById('son');            //如果有父级定位元素
            console.log(box.offsetLeft);//20
            console.log(box.offsetTop); //0
            //如果无父级定位元素
            console.log(box.offsetLeft);//60
            console.log(box.offsetTop); //40
        </script>
    </body></html>复制代码

Copy after login

总结：相对于父元素（看父元素是否有定位，如果有定位，以父元素为基础，如果没有继续往上寻找，如果一直没有找到，则以body为基准）的左边距和上边距

求出当前元素的页面偏移量

要知道某个元素在页面上的偏移量，将这个元素的offsetLeft和offsetTop与其offsetParent的相同属性相加，并加上offsetParent的相应方向的边框，如此循环直到根元素，就可以得到元素到页面的偏移量

<p style="padding: 20px;border:1px solid black;position:absolute;">
    <p id="test" style="width:100px; height:100px; margin:10px;background-color: red;"></p></p><script type="text/javascript">
    var test = document.getElementById('test');    console.log(getElementLeft(test)); //39px
    console.log(getElementTop(test)); // 39px
 
    function getElementLeft(ele){        var actualLeft  = ele.offsetLeft;        var parent = ele.offsetParent;        while (parent != null){
            actualLeft = actualLeft + parent.offsetLeft + parent.clientLeft;
            parent = parent.offsetParent;
        }        return actualLeft + 'px';
    }    function getElementTop(ele){        var actualTop  = ele.offsetTop;        var parent = ele.offsetParent;        while (parent != null){
            actualTop = actualTop + parent.offsetTop + parent.clientTop;
            parent = parent.offsetParent;
        }        return actualTop + 'px';
    }</script>复制代码

Copy after login

client家族

关于元素尺寸，一般地，有偏移大小offset、客户端大小client和滚动大小scroll。前文已经介绍过偏移属性，后文将介绍scroll滚动大小，本文主要介绍客户区大小client。

客户区大小

客户区大小client指的是元素内容及其内边距所占据的空间大小

clientWidth

clientHeight属性返回元素节点的客户区高度

1	`clientHeight = padding-top + height + padding-bottom复制代码`

Copy after login

clientHeight

clientWidth属性返回元素节点的客户区宽度

1	`clientWidth = padding-left + width + padding-right复制代码`

Copy after login

clientLeft

1	`clientLeft属性返回左边框的宽度复制代码`

Copy after login

clientTop

1 2	`clientTop属性返回上边框的宽度` `复制代码`

Copy after login

验证

<p id="box" style="width: 200px;height: 200px;background-color: red; padding: 20px;border: 1px solid orange;"></p><script type="text/javascript">
    var box = document.getElementById('box');    console.log(box.clientWidth);// 200+ 20+ 20 = 240
    console.log(box.clientHeight); //200 + 20 + 20 = 240
    console.log(box.clientLeft);//1
    console.log(box.clientTop);//1</script>复制代码

Copy after login

页面大小

常用document.documentElement的client属性来表示页面大小(不包含滚动条宽度)

1	`document.documentElement.clientWidth;document.documentElement.clientHeight;复制代码`

Copy after login

注意

1.所有的client属性都是只读的

<p id="test" style="width: 100px;height: 100px;padding: 10px;margin: 10px;border: 1px solid black;"></p><script>
    var test = document.getElementById('test');    console.log(test.clientHeight);    //静态失败了
    test.clientHeight = 10;    console.log(test.clientHeight);</script>复制代码

Copy after login

2.如果给元素设置了display:none，则客户区client属性都为0

<p id="test" style="width: 100px;height: 100px;padding: 10px;margin: 10px;border: 1px solid black;display:none;"></p><script>
    var test = document.getElementById('test');    console.log(test.clientHeight);//0
    console.log(test.clientTop);//0</script>复制代码

Copy after login

3.每次访问客户区client属性都需要重新计算，重复访问需要耗费大量的性能，所以要尽量避免重复访问这些属性。如果需要重复访问，则把它们的值保存在变量中，以提高性能

<p id="test" style="width: 100px;height: 100px;padding: 10px;margin: 10px;border: 1px solid black;"></p>      <script>
    var test = document.getElementById('test');    console.time("time");    for(var i = 0; i < 100000; i++){        var a = test.clientHeight;
    }    console.timeEnd('time');//66.798ms</script>复制代码

Copy after login

<p id="test" style="width: 100px;height: 100px;padding: 10px;margin: 10px;border: 1px solid black;"></p>         
<script>
    var test = document.getElementById('test');
    console.time("time");
    var a = test.clientHeight;
    for(var i = 0; i < 100000; i++){
        var b = a;
    }
    console.timeEnd('time');//1.705ms
</script>复制代码

Copy after login

scroll家族

滚动宽高

scrollHeight

　　scrollHeight表示元素的总高度，包括由于溢出而无法展示在网页的不可见部分

scrollWidth

　　scrollWidth表示元素的总宽度，包括由于溢出而无法展示在网页的不可见部分

没有滚动条时，scrollHeight与clientHeight属性结果相等，scrollWidth与clientWidth属性结果相等

<p id="test" style="width: 100px;height: 100px;padding: 10px;margin: 10px;border: 1px solid black;"></p><script>
    var test = document.getElementById('test');    //120 120
    console.log(test.scrollHeight,test.scrollWidth);    //120 120
    console.log(test.clientHeight,test.clientWidth);</script>复制代码

Copy after login

存在滚动条时，但元素设置宽高大于等于元素内容宽高时，scroll和client属性的结果相等

<p id="test" style="width: 100px;height: 100px;padding: 10px;margin: 10px;border: 1px solid black;"></p><script>
    var test = document.getElementById('test');    //120 120
    console.log(test.scrollHeight,test.scrollWidth);    //120 120
    console.log(test.clientHeight,test.clientWidth);</script>复制代码

Copy after login

滚动长度

scrollTop

scrollTop属性表示被隐藏在内容区域上方的像素数。元素未滚动时，scrollTop的值为0，如果元素被垂直滚动了，scrollTop的值大于0，表示元素上方不可见内容的像素高度

scrollLeft

scrollLeft属性表示被隐藏在内容区域左侧的像素数。元素未滚动时，scrollLeft的值为0，如果元素被水平滚动了，scrollLeft的值大于0，且表示元素左侧不可见内容的像素宽度

当滚动条滚动到内容底部时，符合以下等式

1	`scrollHeight = scrollTop + clientHight复制代码`

Copy after login

与scrollHeight和scrollWidth属性不同的是，scrollLeft和scrollTop是可写的

<p id="test" style="width: 100px;height: 100px;padding: 10px;margin: 10px;border: 1px solid black;overflow:scroll;font-size:20px;line-height:200px;">
    内容<br>内容<br></p><button id="btn1">向下滚动</button><button id="btn2">向上滚动</button><script type="text/javascript">
    // scrollLeft和scrollTop是可读写的
    var btn1 = document.getElementById('btn1');    var btn2 = document.getElementById('btn2');
    btn1.onclick =  function (){
        test.scrollTop += 10;
    }
    btn2.onclick =  function (){
        test.scrollTop -= 10;
    }</script>复制代码

Copy after login

页面滚动

理论上，大部分的浏览器通过document.documentElement.scrollTop和scrollLeft可以反映和控制页面的滚动；safari浏览器是通过document.body.scrollTop和scrollLeft来控制的

<body style="height: 2000px;width: 2000px;">
    <p id="test" style="width: 100px;height: 100px;padding: 10px;margin: 10px;border: 1px solid black;overflow:scroll;font-size:20px;line-height:200px;">
        内容<br>内容<br>
    </p>
    <script type="text/javascript">
 
        // 页面滚动
        window.onscroll = function (){            console.log(document.documentElement.scrollTop,document.documentElement.scrollLeft);            console.log(document.body.scrollTop,document.body.scrollLeft);
 
        }    </script></body>复制代码

Copy after login

所以，页面的滚动高度兼容写法是

1	`var` `docScrollTop = document.documentElement.scrollTop \|\| document.body.scrollTop复制代码`

Copy after login

回到顶部

<!DOCTYPE html><html>
    <head>
        <meta charset="utf-8">
        <title></title>
    </head>
    <body style="height: 2000px;">
        <button id="backTop" style="position: fixed;">回到顶部</button>
        <script type="text/javascript">
            var backTop = document.getElementById('backTop');
            backTop.onclick = scrollTop;            function scrollTop(){                //兼容性写法
                if(document.documentElement.scrollTop || document.body.scrollTop){                    document.documentElement.scrollTop = document.body.scrollTop = 0;
                }
            }        </script>
    </body></html>复制代码

Copy after login

滚动方法

scrollTo(x,y)

scrollTo(x,y)方法滚动当前window中显示的文档，让文档中由坐标x和y指定的点位于显示区域的左上角

<body style="height: 2000px;">
    <button id="backTop" style="position: fixed;">回到顶部</button>
    <script src="scrollTop.js" type="text/javascript" charset="utf-8"></script>
    <script type="text/javascript">
        var backTop = document.getElementById('backTop');
        backTop.onclick = scrollTop;        function scrollTop(){
            scrollTo(0,0);
        }    </script></body>复制代码

Copy after login

相关免费学习推荐：javascript（视频）

The above is the detailed content of Introducing the offset, client, and scroll family properties of JavaScript. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress images for free

Clothoff.io

AI clothes remover

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Assassin's Creed Shadows: Seashell Riddle Solution

3 weeks ago By DDD

What's New in Windows 11 KB5054979 & How to Fix Update Issues

2 weeks ago By DDD

Where to find the Crane Control Keycard in Atomfall

3 weeks ago By DDD

Assassin's Creed Shadows - How To Find The Blacksmith And Unlock Weapon And Armour Customisation

4 weeks ago By DDD

Roblox: Dead Rails - How To Complete Every Challenge

3 weeks ago By DDD

Hot Tools

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Hot Topics

Where is the login entrance for gmail email?

7584

CakePHP Tutorial

1386

What is the format of the account name of steam

win11 activation key permanent

nyt connections hints and answers

123

Related knowledge

How to implement an online speech recognition system using WebSocket and JavaScript Dec 17, 2023 pm 02:54 PM

How to use WebSocket and JavaScript to implement an online speech recognition system Introduction: With the continuous development of technology, speech recognition technology has become an important part of the field of artificial intelligence. The online speech recognition system based on WebSocket and JavaScript has the characteristics of low latency, real-time and cross-platform, and has become a widely used solution. This article will introduce how to use WebSocket and JavaScript to implement an online speech recognition system.

WebSocket and JavaScript: key technologies for implementing real-time monitoring systems Dec 17, 2023 pm 05:30 PM

WebSocket and JavaScript: Key technologies for realizing real-time monitoring systems Introduction: With the rapid development of Internet technology, real-time monitoring systems have been widely used in various fields. One of the key technologies to achieve real-time monitoring is the combination of WebSocket and JavaScript. This article will introduce the application of WebSocket and JavaScript in real-time monitoring systems, give code examples, and explain their implementation principles in detail. 1. WebSocket technology

How to use JavaScript and WebSocket to implement a real-time online ordering system Dec 17, 2023 pm 12:09 PM

Introduction to how to use JavaScript and WebSocket to implement a real-time online ordering system: With the popularity of the Internet and the advancement of technology, more and more restaurants have begun to provide online ordering services. In order to implement a real-time online ordering system, we can use JavaScript and WebSocket technology. WebSocket is a full-duplex communication protocol based on the TCP protocol, which can realize real-time two-way communication between the client and the server. In the real-time online ordering system, when the user selects dishes and places an order

How to implement an online reservation system using WebSocket and JavaScript Dec 17, 2023 am 09:39 AM

How to use WebSocket and JavaScript to implement an online reservation system. In today's digital era, more and more businesses and services need to provide online reservation functions. It is crucial to implement an efficient and real-time online reservation system. This article will introduce how to use WebSocket and JavaScript to implement an online reservation system, and provide specific code examples. 1. What is WebSocket? WebSocket is a full-duplex method on a single TCP connection.

JavaScript and WebSocket: Building an efficient real-time weather forecasting system Dec 17, 2023 pm 05:13 PM

JavaScript and WebSocket: Building an efficient real-time weather forecast system Introduction: Today, the accuracy of weather forecasts is of great significance to daily life and decision-making. As technology develops, we can provide more accurate and reliable weather forecasts by obtaining weather data in real time. In this article, we will learn how to use JavaScript and WebSocket technology to build an efficient real-time weather forecast system. This article will demonstrate the implementation process through specific code examples. We

Simple JavaScript Tutorial: How to Get HTTP Status Code Jan 05, 2024 pm 06:08 PM

JavaScript tutorial: How to get HTTP status code, specific code examples are required. Preface: In web development, data interaction with the server is often involved. When communicating with the server, we often need to obtain the returned HTTP status code to determine whether the operation is successful, and perform corresponding processing based on different status codes. This article will teach you how to use JavaScript to obtain HTTP status codes and provide some practical code examples. Using XMLHttpRequest

How to use insertBefore in javascript Nov 24, 2023 am 11:56 AM

Usage: In JavaScript, the insertBefore() method is used to insert a new node in the DOM tree. This method requires two parameters: the new node to be inserted and the reference node (that is, the node where the new node will be inserted).

JavaScript and WebSocket: Building an efficient real-time image processing system Dec 17, 2023 am 08:41 AM

JavaScript is a programming language widely used in web development, while WebSocket is a network protocol used for real-time communication. Combining the powerful functions of the two, we can create an efficient real-time image processing system. This article will introduce how to implement this system using JavaScript and WebSocket, and provide specific code examples. First, we need to clarify the requirements and goals of the real-time image processing system. Suppose we have a camera device that can collect real-time image data

See all articles