【温故而知新-Javascript】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:Luka

Name:weather Value:sunny

Name: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>