Arithmetic Operators

Having explained operator precedence, associativity, and other background material, it’s time to discuss the operators themselves. This section details the arithmetic operators:
Addition (+)
The + operator adds numeric operands or concatenates string operands. If one operand is a string, the other is converted to a string, and the two strings are then concatenated. Object operands are converted to numbers or strings that can be added or concatenated. The conversion is performed by the valueOf( ) method and/or the toString( ) method of the object.
Subtraction (-)
When - is used as a binary operator, it subtracts its second operand from its first operand. If used with nonnumeric operands, it attempts to convert them to numbers.
Multiplication (*)
The * operator multiplies its two operands. If used with nonnumeric operands, it attempts to convert them to numbers.
Division (/)
The / operator divides its first operand by its second. If used with nonnumeric operands, it attempts to convert them to numbers. If you are used to programming languages that distinguish between integer and floating-point numbers, you might expect to get an integer result when you divide one integer by another. In JavaScript, however, all numbers are floating-point, so all division operations have floating-point results: 5/2 evaluates to 2.5, not 2. Division by zero yields positive or negative infinity, while 0/0 evaluates to NaN.
Modulo (%)
The % operator computes the first operand modulo the second operand. In other words, it returns the remainder when the first operand is divided by the second operand a certain number of times. If used with nonnumeric operands, the modulo operator attempts to convert them to numbers. The sign of the result is the same as the sign of the first operand. For example, 5 % 2 evaluates to 1.
While the modulo operator is typically used with integer operands, it also works for floating-point values. For example, -4.3 % 2.1 evaluates to -0.1.
Unary minus (-)
When - is used as a unary operator, before a single operand, it performs unary negation. In other words, it converts a positive value to an equivalently negative value, and vice versa. If the operand is not a number, this operator attempts to convert it to one.
Unary plus (+)
For symmetry with the unary minus operator, JavaScript also has a unary plus operator. This operator allows you to explicitly specify the sign of numeric literals, if you feel that this will make your code clearer:
var profit = +1000000;
In code like this, the + operator does nothing; it simply evaluates to the value of its argument. Note, however, that for nonnumeric arguments, the + operator has the effect of converting the argument to a number. It returns NaN if the argument cannot be converted.
Increment (++)
The ++ operator increments (i.e., adds 1 to) its single operand, which must be a variable, an element of an array, or a property of an object. If the value of this variable, element, or property is not a number, the operator first attempts to convert it to one. The precise behavior of this operator depends on its position relative to the operand. When used before the operand, where it is known as the pre-increment operator, it increments the operand and evaluates to the incremented value of that operand. When used after the operand, where it is known as the post-increment operator, it increments its operand but evaluates to the unincremented value of that operand. If the value to be incremented is not a number, it is converted to one by this process.
For example, the following code sets both i and j to 2:
i = 1;

j = ++i;
But these lines set i to 2 and j to 1:
i = 1;

j = i++;
This operator, in both of its forms, is most commonly used to increment a counter that controls a loop. Note that, because of JavaScript’s automatic semicolon insertion, you may not insert a line break between the post-increment or post-decrement operator and the operand that precedes it. If you do so, JavaScript will treat the operand as a complete statement by itself and insert a semicolon before it.
Decrement (–)
The – operator decrements (i.e., subtracts 1 from) its single numeric operand, which must be a variable, an element of an array, or a property of an object. If the value of this variable, element, or property is not a number, the operator first attempts to convert it to one. Like the ++ operator, the precise behavior of – depends on its position relative to the operand. When used before the operand, it decrements and returns the decremented value. When used after the operand, it decrements the operand but returns the undecremented value.
<script> 
 function getAnchor(str) 
 { 
 window.location.hash=str; 
 } 
</script> 
<body> 
 //创建锚点链接，快速定位网页内容
 <a href="javascript:getAnchor('java');">java</a> 
 <a href="javascript:getAnchor('java');">java</a> 
 <a href="javascript:getAnchor('java');">java</a> 
 //下面定义了3个锚点
 <a name="java"><center>java</center> 
 <!--java--> 
 </a><br><br><br><br><br> 
 <a name="java"><center>java</center> 
 <!--java--> 
 </a><br><br><br><br><br> 
 <a name="java"><center>java</center> 
 <!--java--> 
 </a> 
</body>

1、设置锚点 
把光标置于文档窗口想要设置锚点的地方（就是你所说的页面顶端）点击插入面板中”常用”／”常用锚记”。在弹出的对话框中起一个锚名字（如aa） 
2、创建锚点链接 
选择要建立链接的文本或图像，在属性面板的链接中输入一个#号和锚点名。（例如：#aa） 要链向不同页面中的锚点，则点击链接边的文件夹小图标，在打开对话框中选择要链接的文件，按"确定"键后在"属性"面板的链接栏中会显示链接的文件地址，在地址后面紧跟着输入＃号和锚名字





<body>
下方输入
<a name="#如d"></a>

页面中任意位置输入如下代码,如
<a href="#d">Top</a>

通俗简单地说，比如一篇很长的文章，你想按分段精确来看，那就可以用到锚点了。 命名锚记像一个迅速定位器一样是一种页面内的超级链接，运用相当普遍。 

一，HTML 页面锚点的两种方式。（无动效）


1，创建锚点使用 <a> （锚）标签和 name 属性
      a,同一页面内
              <a href="#001">跳到001</a> 
              ...文字省略 
             <a name="001" > & n b s p </a> 
              ...文字省略 


      b，不同页面
             <a href="123.html#001">跳到001</a> 
             ...文字省略 
            <a name="001" > & n b s p </a> 
            ...文字省略 


2，标签 name 属性之外，还可以使用 id 属性（与上述类似）

       a,同一页面内
              <a href="#001">跳到001</a> 

             ...文字省略 

              <div  id="001" >内容 </div> 

              ...文字省略 


       b，不同页面
             <a href="123.html#001">跳到001</a> 

            ...文字省略 

            <div  id="001" >内容  </div> 

           ...文字省略 


二，利用jq的animate是想动效锚点链接
导航栏自定义属性

<ul class="index_nav">
    <li><a href="javascript:void(0)" title="1"></a></li>
    <li><a href="javascript:void(0)" title="2"></a></li>
</ul>


内容块相应id名

<div class="row" id="index_1">
    <h2 >这是第一一个活动页</h2>
    <div class="mainpage mainpage1"></div>
</div>

<div class="row" id="index_2">
    <h2 >这是第二二个活动页</h2>
    <div class="mainpage mainpage2"></div>
</div>



<script>
    $(function(){
        $(".index_nav li a").click(function() {
            var index=this.title;
            var id='#index_'+index;
            //alert(id)
            $("html,body").animate({scrollTop: $(id).offset().top}, 1000);
        })
    })
</script>

锚点是文档中某行的一个记号，类似于书签，用于链接到文档中的某个位置。当定义了锚点后，我们可以创建直接跳至该锚点（比如页面中某个小节）的链接，这样使用者就无需不停地滚动页面来寻找他们需要的信息了。 

在使用<a>元素创建锚点时，需要使用 name 属性为其命名，代码如下所示：



<a name=”anchorname1”>锚点一</a>

然后就可以创建链接，直接跳转到锚点，代码如下所示：



<a href=”#anchorname1”>回到锚点一</a>