Summary of BOM related knowledge points in JS (must read)-JS Tutorial-php.cn

Home

Web Front-end

JS Tutorial

Summary of BOM related knowledge points in JS (must read)

高洛峰

Dec 06, 2016 am 09:52 AM

Window object

ECMAScript is the core of JavaScript, but if you want to use JavaScript in the web, then the BOM (Browser Object Model) is the real core. The BOM provides a number of objects for accessing browser functionality that are independent of any web page content.

window object: The core object of BOM is window, which represents an instance of the browser. In the browser, the window object has a dual role. It is not only an interface for accessing the browser window through javascript, but also a Global object specified by ECMAScript.

Therefore, all variables and functions declared in the global scope will become properties and methods of the window object.

<script type="text/javascript">
  var age=26;//这里定义的全局变量和全局函数被自动归在了window对象名下
  function sayAge(){
    console.log(this.age);
  }
  console.log(window.age);//26
  sayAge();//26 相当于window.sayAge()
  window.sayAge();//26
 
  //全局变量和在window对象上直接定义属性的唯一区别：全局变量不能够通过delete操作符删除，而直接在window对象上定义的属性可以
  window.color=&#39;red&#39;;
  delete window.age;
  delete window.color;
  console.log(window.age);//26
  console.log(window.color);//undefined
  </script>

<script type="text/javascript">
    /*
    还要注意：尝试访问未声明的变量会抛出错误，但是通过查询window对象，可以知道某个可能未经声明的变量是否存在
     */
    //这会抛出错误，因为oldValue未定义
    var newValue=oldValue;
    //这不会抛出错误，因为是一次属性查询
    var newValue=window.oldValue;
  </script>

Window relationships and frames

If the page contains frames, each frame has its own window object and is saved in the frames collection. In the frames collection, the corresponding window object can be accessed by numerical index (starting from 0, left to right, top to bottom) or frame name. Each window object has a name attribute, which contains the name of the frame.

You can reference the upper frame through window.frames[0] or window.frames["topFrame"]. However, it is better to use top instead of window to refer to these frames. Because the top object always points to the highest (outermost) frame, which is the browser window. Use this to ensure correct access from one frame to another. Because for any code written in a framework, the window object points to a specific instance of that framework, not the highest-level framework.

Another window object opposite to top is parent. The parent object always points to the frame directly above the current frame.

The last object related to the frame is self, which always points to the window. self and window objects can be used interchangeably.

When using frames, there will be multiple Global objects in the browser. Global variables defined in each frame automatically become properties of the window object in the frame. Since each window object contains a native type constructor, each framework has its own set of constructors, which correspond to each other but are not equal.

location object

The location object is a very special object because it is an attribute of both the window object and the document object. window.location and document.location refer to the same object.

Attributes of the location object:

Summary of BOM related knowledge points in JS (must read)

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>查询字符串参数</title>
</head>
<body>
<script type="text/javascript">
    function getQueryStringArgs(){
      //取得查询字符串并去掉开头的问号
      var qs = (location.search.length > 0 ? location.search.substring(1) : ""),
        //保存数据对象
        args = {},
        //取得每一项
        items = qs.length ? qs.split("&") : [],
        item = null,
        name = null,
        value = null,
        //在for循环中使用
        i = 0,
        len = items.length;
      //逐个将每一项添加到args对象中
      for (i=0; i < len; i++){
        item = items[i].split("=");
        //decodeURIComponent用来解码name和value,因为查询字符串应该是被编码过的
        name = decodeURIComponent(item[0]);
        value = decodeURIComponent(item[1]);
 
        if (name.length){
          args[name] = value;
        }
      }
      return args;
    }
    //假设查询字符串是： ?q=javascript&num=10
    var args = getQueryStringArgs();
    alert(args["q"]);   //"javascript"
    alert(args["num"]);  //"10"
    //这样一来，每个查询字符串参数都成了返回对象的属性，极大地方便了对每个参数的访问
</script>
</body>
</html>

Using the location object, you can change the location of the browser in many ways.

Among them, the most common way is: use the assign() method and pass it a URL

location.assign("http://www.php.cn")

This way you can open the new URL immediately and Generates a record in the browser's history.

Similarly, setting location.href and window.location to a URL value will also call the assign() method with this value.

location.href=”http://www.php.cn”;
window.location=”http://www.php.cn”;

The effect and display of these two methods call the assign() method The effect is exactly the same

In addition, the currently loaded page can also be changed by modifying other properties of the location object.

Summary of BOM related knowledge points in JS (must read)

Every time you modify the location attributes (except hash), the page will be reloaded with a new URL. Modifying the hash value will generate a new record in the browser's history. The '#helloworld' in the URL: http://a.com#helloword is location.hash. Changing the hash will not cause the page to refresh. , so hash values can be used for data transfer. Of course, the data capacity is limited.

When the URL is modified through any of the above methods, a new record will be generated in the browser's history, so clicking the "Back" button will navigate to the previous page.

We can use the replace() method to disable this behavior. This method only accepts one parameter, which is the URL to be navigated to; although the result will cause the browser location to change, it will not generate a new record in the history. After calling the replace() method, the user cannot return to the previous page.

After this page is loaded into the browser, the browser will redirect to www.php.cn after 1 second. The 'Back' button will then be disabled and you will not be able to return to the example page if you re-enter the full URL.

<script type="text/javascript">
    setTimeout(function () {
      location.replace("http://www.php.cn/");
    }, 1000);
  </script>

reload() method, its function is to reload the currently displayed page. If you call the reload() method without passing any parameters, the page will be reloaded in the most efficient way. That is, if the page has not changed since the last request, the page will be reloaded from the browser cache. If you want to force a reload from the server, you need to pass the parameter true to this method.

location.reload();//Reload (possibly load from cache)

location.reload(true);//Reload (reload from server)

Timeout call and intermittent call

javascript是单线程语言，但允许通过设置超时值和间歇值来设定代码在特定时刻执行

超时调用：是在指定的时间过后执行代码

间歇调用：每隔指定的时间就执行一次代码

超时调用：需要使用window对象的setTimeout()方法，接收两个参数：要执行的代码和以毫秒表示的时间。

第二个参数是一个表示等待多长时间的毫秒数，但经过该时间后指定的代码不一定执行。因为，javascript是一个单线程的解释器，因此一定时间内只能执行一段代码。第二个参数表示再过多长时间把当前任务添加到队列中。如果队列是空的，则代码会立刻执行，否则就要等待前面的代码执行完了以后再执行。

调用setTimeout()后，该方法会返回一个数值ID,表示超时调用。要取消未执行的超时调用计划，可以调用clearTimeout()方法并将相应的超时调用ID作为参数传递给它即可。

间歇调用：使用setInterval()方法

与超时调用类似，只不过它会按照指定的时间间隔重复执行代码，直到间歇调用被取消或者页面被卸载。它接收的参数与setTimeout()方法一样

Demo1

<script type="text/javascript">
    //设置超时调用
    var timeoutId = setTimeout(function() {
      alert("Hello world!");
    }, 1000);
    //取消超时调用
    clearTimeout(timeoutId);
  </script>

Demo2

<script type="text/javascript">
  /*
  使用间歇调用实现
   */
    var num = 0;
    var max = 10;
    var intervalId = null;
    function incrementNumber() {
      num++;
      if (num == max) {
        clearInterval(intervalId);
        alert("Done");
      }
    }
    intervalId = setInterval(incrementNumber, 500);
  </script>

Demo3

   
<script type="text/javascript">
  /*
  使用超时调用来实现
   */
    var num = 0;
    var max = 100;
    function incrementNumber() {
      num++;
      if (num < max) {
        setTimeout(incrementNumber, 500);
      } else {
        alert("Done");
      }
    }
    setTimeout(incrementNumber, 500);
  </script>

在使用超时调用时，没有必要跟踪超时调用ID，因为每次执行代码之后，如果不再设置另一次超时调用，调用就会自动停止。一般认为，使用超时调用来模拟间歇调用是一种最佳模式。间歇调用一般较少使用，因为后一个间歇调用可能会在前一个间歇调用结束之前启动。

系统对话框

alert()、confirm()和prompt()

<script type="text/javascript">
    alert("Hello world!");
  </script>
 
 
 
<script type="text/javascript">
  /*
  判断用户点击了OK还是Cancel，可以检查confirm()方法返回的布尔值：true表示单击了OK，false表示单击了Cancel或单击了右上角的X按钮。
   */
    if (confirm("Are you sure?")) {
      alert("I&#39;m so glad you&#39;re sure! ");
    } else {
       alert("I&#39;m sorry to hear you&#39;re not sure. ");
    }
  </script>
 
 
 
<script type="text/javascript">
  /*
  prompt()方法用来生成一个"提示"框，用于提示用户输入一些文本。提示框除了显示OK和Cancel按钮之外 ，还会显示一个文本输入域，用来输入文本内容。该方法接收两个参数：要显示给用户的文本提示和文本输入域的默认值(可以是一个空字符串)
   */
    var result = prompt("What is your name? ", "");
    if (result !== null) {
     alert("Welcome, " + result);
    }
  </script>

history对象

history对象保存着用户上网的历史记录，从窗口被打开的那一刻算起。因为history是window对象的属性，因此每个浏览器窗口、每个标签页以及每个框架，都有自己的history对象与特定的window对象关联。处于安全方面的考虑，开发人员是无法知道用户浏览过的URL，不过，借助用户访问过的页面列表，同样可以在不知道实际URL的情况下实现后退和前进。

使用Go()方法可以在用户的历史记录中任意跳转，可以向后也可以向前。该方法接收一个参数：表示向前或者向后跳转的页面数的整数值。负数表示向后跳转(类似单击浏览器的后退按钮)，正数表示向前跳转(类似浏览器的前进按钮)。

//后退一页
    history.go(-1);
    //前进一页
    history.go(1);

也可以给go()方法传递一个字符串参数，此时浏览器会跳转到历史记录中包含该字符串的第一个位置–可能后退也可能前进，具体要看哪个位置最近。如果历史记录中不包含该字符串，那么这个方法什么也不做

//跳转到最近的php.cn
history.go("php.cn");

另外，还可以使用back()和forward()来代替go()方法

//后退一页
    history.back();
    //前进一页
    history.forward();

除此之外，history对象还有一个length属性，保存着历史记录的数量。这个数量包括所有的历史记录，即所有的向后和向前的记录。如果history.length==0，则表示这是用户打开窗口后的第一个页面

history对象不常用，但是在创建自定义的后退和前进按钮，以及检测当前页面是不是用户历史记录的第一个页面时，还是必须使用它。

Demo1

history.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>history</title>
</head>
<body>
  <form>
    <input type="text" id="username">
  </form>
  <input type="button" id="btn" value="按钮" onclick="go()">
  <script type="text/javascript">
    function go(){
      var name=document.getElementById("username").value;
      if(name=="hello"){
        history.go(-1);
      }else{
        alert(&#39;用户名不正确&#39;);
      }
    }
  </script>
</body>
</html>

ceshi.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title></title>
  <link rel="stylesheet" href="">
</head>
<body>
  <a href="history.html" >跳转</a>
</body>
</html>

这里使用history模仿了一个输入用户名之后。跳转到之前页面的例子。

Demo2
history2.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>history</title>
</head>
<body>
  <a href="demo.html">跳转</a>
  <input type="button" id="btn" value="前进" onclick="go()">
  <script type="text/javascript">
    function go(){
      history.forward();
    }
  </script>
</body>
</html>

demo.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title></title>
  <link rel="stylesheet" href="">
</head>
<body>
  <input type="button" name="" value="回退" id="btn" onclick="fn()">
  <script type="text/javascript">
    function fn(){
      history.back();
    }
  </script>
</body>
</html>

这个小例子模拟了history.back()和history.forward()的基本功能

Statement

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

如何使用JS和百度地图实现地图平移功能Nov 21, 2023 am 10:00 AM

如何使用JS和百度地图实现地图平移功能百度地图是一款广泛使用的地图服务平台，在Web开发中经常用于展示地理信息、定位等功能。本文将介绍如何使用JS和百度地图API实现地图平移功能，并提供具体的代码示例。一、准备工作使用百度地图API前，首先需要在百度地图开放平台（http://lbsyun.baidu.com/）上申请一个开发者账号，并创建一个应用。创建完成

js字符串转数组Aug 03, 2023 pm 01:34 PM

js字符串转数组的方法：1、使用“split()”方法，可以根据指定的分隔符将字符串分割成数组元素；2、使用“Array.from()”方法，可以将可迭代对象或类数组对象转换成真正的数组；3、使用for循环遍历，将每个字符依次添加到数组中；4、使用“Array.split()”方法，通过调用“Array.prototype.forEach()”将一个字符串拆分成数组的快捷方式。

如何使用JS和百度地图实现地图热力图功能Nov 21, 2023 am 09:33 AM

如何使用JS和百度地图实现地图热力图功能简介：随着互联网和移动设备的迅速发展，地图成为了一种普遍的应用场景。而热力图作为一种可视化的展示方式，能够帮助我们更直观地了解数据的分布情况。本文将介绍如何使用JS和百度地图API来实现地图热力图的功能，并提供具体的代码示例。准备工作：在开始之前，你需要准备以下事项：一个百度开发者账号，并创建一个应用，获取到相应的AP

如何使用JS和百度地图实现地图多边形绘制功能Nov 21, 2023 am 10:53 AM

如何使用JS和百度地图实现地图多边形绘制功能在现代网页开发中，地图应用已经成为常见的功能之一。而地图上绘制多边形，可以帮助我们将特定区域进行标记，方便用户进行查看和分析。本文将介绍如何使用JS和百度地图API实现地图多边形绘制功能，并提供具体的代码示例。首先，我们需要引入百度地图API。可以利用以下代码在HTML文件中导入百度地图API的JavaScript

js中new操作符做了哪些事情Nov 13, 2023 pm 04:05 PM

js中new操作符做了：1、创建一个空对象，这个新对象将成为函数的实例；2、将新对象的原型链接到构造函数的原型对象，这样新对象就可以访问构造函数原型对象中定义的属性和方法；3、将构造函数的作用域赋给新对象，这样新对象就可以通过this关键字来引用构造函数中的属性和方法；4、执行构造函数中的代码，构造函数中的代码将用于初始化新对象的属性和方法；5、如果构造函数中没有返回等等。

用JavaScript模拟实现打字小游戏！Aug 07, 2022 am 10:34 AM

这篇文章主要为大家详细介绍了js实现打字小游戏，文中示例代码介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们可以参考一下。

php可以读js内部的数组吗Jul 12, 2023 pm 03:41 PM

php在特定情况下可以读js内部的数组。其方法是：1、在JavaScript中，创建一个包含需要传递给PHP的数组的变量；2、使用Ajax技术将该数组发送给PHP脚本。可以使用原生的JavaScript代码或者使用基于Ajax的JavaScript库如jQuery等；3、在PHP脚本中，接收传递过来的数组数据，并进行相应的处理即可。

js是什么编程语言？May 05, 2019 am 10:22 AM

js全称JavaScript，是一种具有函数优先的轻量级，直译式、解释型或即时编译型的高级编程语言，是一种属于网络的高级脚本语言；JavaScript基于原型编程、多范式的动态脚本语言，并且支持面向对象、命令式和声明式，如函数式编程。

See all articles

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

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)

2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

How Long Does It Take To Beat Split Fiction?

1 months agoByDDD

R.E.P.O. Save File Location: Where Is It & How to Protect It?

1 months agoByDDD

R.E.P.O. Best Graphic Settings

2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Assassin's Creed Shadows: Seashell Riddle Solution

1 weeks agoByDDD

Hot Tools

SAP NetWeaver Server Adapter for Eclipse

Integrate Eclipse with SAP NetWeaver application server.

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool

DVWA

Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software