学习笔记-js-2017.2.25

一、HTML DOM 元素(节点)

1、创建新的 HTML 元素
如需向 HTML DOM 添加新元素，您必须首先创建该元素（元素节点），然后向一个已存在的元素追加该元素。

<div id="div1">
    <p id="p1">1</p>
    <p id="p2">2</p>
</div>
<script type="text/javascript">
    var para =document.createElement("p");
    var node =document.createTextNode("这是一个新段落。");
    para.appendChild(node);
    var element=document.getElementById("div1");
    element.appendChlid(para);
</script>

2、删除已有的 HTML 元素

<div id="div1">
<p id="p1">1</p>
<p id="p2">2</p>
</div>
<script type="text/javascript">
    var parent=document.getElementById("div1");
    var child=document.getElementById("p1");
    parent.removeChild(child);
</script>

二、JavaScript 对象

1、访问对象的属性

objectName.propertyName

2、访问对象的方法

objectName.methodName()

3、使用对象构造器

<div id="div1">
<p id="p1">1</p>
<p id="p2">2</p>
</div>
<script type="text/javascript">
    var person=new Object();
    person.firstname="John";
    person.lastname="Doe";
    person.age=50;
    person.eyecolor="blue";
    document.write(person.firstname+" is "+person.age+" years old.");
</script>

4、把属性添加到 JavaScript 对象

person.firstname="John";
person.lastname="Doe";
person.age=30;
person.eyecolor="blue";
x=person.firstname;

5、把方法添加到 JavaScript 对象

<script>
    function person(firstname,lastname,age,eyecolor){
    this.firstname=firstname;
    this.lastname=lastname;
    this.age=age;
    this.eyecolor=eyecolor;
    this.changeName=changeName;
    function changeName(name){
        this.lastname=name;
    }
}
    myMother=new person("Sally","Rally",48,"green");
    myMother.changeName("Doe");
    document.write(myMother.lastname);
</script>

6、JavaScript for...in 循环

语法

for (variable in object)
{
    执行的代码……
}

for...in 循环中的代码块将针对每个属性执行一次。

<button onclick="myFunction()">点击</button>
<p id="demo"></p>
<script type="text/javascript">
    function myFunction(){
        var x;
        var txt="";
        var person={fname:"Bill",lname:"Gates",age:56};
        for (x in person){
        txt=txt + person[x];
    }
        document.getElementById("demo").innerHTML=txt;
    }
</script>

三、JavaScript Number 对象

1、

<button onclick="myFunction()">点击</button>
<p id="demo"></p>
<script type="text/javascript">
  function myFunction(){
    var x=2+3;
    document.getElementById("demo").innerHTML=x;
    }
 </script>

2、

<script type="text/javascript">
        var myNumber=128;
        document.write(myNumber);
        document.write(myNumber.toString(16));
        document.write(myNumber.toString(8));
        document.write(myNumber.toString(2));
    </script>

3、

<script type="text/javascript">
        var carname1="a";
        var carname2="b";
        var answer1="c";
        var answer2="d";
        var answer3="e";
        document.write(carname1+"<br>")
        document.write(carname2+"<br>")
        document.write(answer1+"<br>")
        document.write(answer2+"<br>")
        document.write(answer3+"<br>")
    </script>