JavaScript built-in objects-JS Tutorial-php.cn

JavaScript built-in objects

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Release： 2016-12-20 14:33:18

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Array array
var myArray = new Array(); //Create an empty array
var myArray = new Array(5); //Create an array of size 5. At this time, if myArray[0] is directly referenced, undefined will be returned .
var myArray = new (0,1,2,3); //Create an array with an initial value of 0123
var myArray = [0,1,2,3]; //Create an array with an initial value of 0123
array As long as it is created, its length can be changed. For example, if you create an array with a length of 5, you can assign subscripts to 5, 6, etc., and the length will automatically change accordingly.

But if you just declare var myArray; you cannot refer to any element in the array, otherwise an error will occur.

You should pay attention here to the difference between new Array(5) and new Array("5"). The former represents creating an array with a size of 5, and the latter represents creating an array with a size of 1 and an initial value of the string 5.

Arrays in JavaScript can store different types of data. For example, an array can store integers and strings at the same time.
The properties of the array are:
constructor: the constructor that references the array
length: returns the number of array elements. If the size of the array is specified when creating the array, this size will be returned regardless of whether the array is assigned a value.
prototype: used to add new properties and methods when defining an array.
The methods of arrays are:
concat (merging arrays), pop(), delete the last element of the array, the length is automatically reduced by 1, reverse, push, shift, etc.

Object object

It is the parent object of all objects. All objects inherit from it, so the properties and methods it has are shared by other objects.
Properties of Object:
constructor: the constructor of the reference array
prototype: add new properties and methods.

Object methods are:
valueOf(): Returns the original value of the object
toString(): Used to convert a function into a string. The following is an example of the object object:

<HTML>
<HEAD>
<TITLE>使用Object的示例</TITLE>
<SCRIPT LANGUAGE="JavaScript" TYPE="text/javascript">
var obj1=new Object(false);
document.write("obj1=new Object(false)"+"<BR>");
document.write("obj1.constructor="+obj1.constructor+"<BR>");
document.write("obj1.valueOf()="+obj1.valueOf()+"<BR>");
document.write("obj1.toString()="+obj1.toString()+"<BR>");
var obj2=new Object("Hello World!");
document.write("obj2=new Object(&#39;Hello World!&#39;)"+"<BR>");
document.write("obj2.constructor="+obj2.constructor+"<BR>");
document.write("obj2.valueOf()="+obj2.valueOf()+"<BR>");
document.write("obj2.toString()="+obj2.toString()+"<BR>");
</SCRIPT>
</HEAD>
<BODY>
</BODY>
</HTML>

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Execution result:
obj1=new Object( false)
obj1.constructor= function Boolean() { [native code] }
obj1.valueOf()=false
obj1.toString()=false
obj2=new Object('Hello World!')
obj2.constructor= function String() { [native code] }
obj2.valueOf()=Hello World!
obj2.toString()=Hello World!

window object
is the current browser window object, including document, navigator, location , history and other sub-objects.

Attributes of the window object:
closed, document, frames, history, length (the number of frames in the current window), location, name, opener,

status (status bar), self (current window), top (top) first floor window).
There are also many methods, such as alert, confirm, blur, etc.

navigator object
is used to obtain various information about the current browser, mainly used to determine what browser the client is using. The example is as follows:

<HTML>
<HEAD>
  <TITLE>navigator示例</TITLE>
<HEAD>
<BODY>
<script language="javascript">
document.write("浏览器代码名称："+navigator.appCodeName+"<BR>");
document.write("浏览器名称："+navigator.appName+"<BR>");
document.write("浏览器版本号："+navigator.appVersion+"<BR>");
document.write("是否支持java："+navigator.javaEnabled()+"<BR>");
document.write("MIME类型数："+navigator.mimeTypes.length+"<BR>");
document.write("操作系统平台："+navigator.platform+"<BR>");
document.write("插件数："+navigator.plugins.length+"<BR>");
document.write("用户代理："+navigator.userAgent+"<BR>");
</script>
</BODY>
</HTML>

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Execution results in IE browser:
Browser code name: Mozilla
Browser name: Microsoft Internet Explorer
Browser version number: 4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727;

.NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET CLR 1.1.4322; InfoPath.2)
Support java: true
Number of MIME types: 0
Operating system platform ：Win32
Number of plug-ins: 0
User agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727;

.NET CLR 3.0.4506.2152; .NET CLR 3.5.30729 ; .NET CLR 1.1.4322; InfoPath.2)

In addition, there are location objects, history objects, and screen objects