【Javascript 基础】对象

1 创建对象

Javascript 支持对象的概率。有多种方法可以用来创建对象。

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <title>Javascript Object </title></head><body><script>  var myData = new Object();  myData.name = "Luka";  myData.weather = "sunny";  document.writeln("Hello "+myData.name+".");  document.writeln("Today is "+myData.weather+".")</script></body></html>

输出结果：

Hello Luka. Today is sunny.

1.1 使用对象字面量

用对象字面向量的方式可以一口气定义一个对象及其属性。

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <title>Javascript Object </title></head><body><script>  var myData = {    name:"Luka",    weather:"sunny"  };  document.writeln("Hello "+myData.name+".");  document.writeln("Today is "+myData.weather+".")</script></body></html>

1.2 将函数用作方法

对象可以添加属性，也能添加函数。属于一个对象的函数称为其方法。

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <title>Javascript Object </title></head><body><script>  var myData = {    name:"Luka",    weather:"sunny",    printMessage:function(){      document.writeln("Hello "+this.name+".");      document.writeln("Today is "+this.weather+".")    }  };  myData.printMessage();</script></body></html>

2 使用对象

创建对象后，可以用来做许多事。

2.1 读取和修改属性值

对象最显而易见的操作是读取或修改属性值

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <title>Javascript Object </title></head><body><script>  var myData = {    name:"Luka",    weather:"sunny"  };   myData.name="Joe";  myData["weather"]="raining";  document.writeln("Hello "+myData.name+".");  document.writeln("It is "+myData["weather"]+".");</script></body></html>

输出结果：

Hello Joe. It is raining.

2.2 枚举对象

要枚举对象属性可以使用 for...in 语句。

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <title>Javascript Object </title></head><body><script>  var myData = {    name:"Luka",    weather:"sunny",    printMessages:function(){      document.writeln("Hello "+this.name+". ");      document.writeln("Today is "+this.weather+".");    }  };  for(var prop in myData){    document.writeln("Name: "+prop+" Value: "+myData[prop]+"<br />");  }</script></body></html>

显示结果：

Name:name Value:LukaName:weather Value:sunnyName:printMessages Value:function (){ document.writeln("Hello "+this.name+". "); document.writeln("Today is "+this.weather+"."); }

2.3 增删属性和方法

就算是用对象字面量生成的对象，也可以为其定义新属性。

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <title>Javascript Object </title></head><body><script>  var myData = {    name:"Luka",    weather:"sunny"  };  //为对象添加新属性  myData.dayOfWeek = "Monday";  //为对象添加新方法  myData.sayHello = function(){    document.writeln("Hello");  };  //对象的属性和方法可以用 delete 关键字删除  delete myData.name;  delete myData["weather"];  delete myData.sayHello;</script></body></html>

2.4 判断对象是否具有某个属性

可以用 in 表达式判断对象是否具有某个对象。

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <title>Javascript Object </title></head><body><script>  var myData = {    name:"Luka",    weather:"sunny"  };  var hasName = "name" in myData;  var hasDate = "date" in myData;  document.writeln("HasName: "+hasName+"<br />");  document.writeln("HasDate: "+hasDate);</script></body></html>

输出结果：