javascript初步.

javascript:

<wbr>一、和java不同之处：<br><wbr>1、所属公司不一样，是NetScape公司的语言,基于对象和事件驱动；java是sun公司的，现在是oracle公司的.<br><wbr>2、js是基于对象，java是面向对象.<br><wbr>3、js是由浏览器解释并执行，java由jvm解释并执行.<br><wbr>4、js是弱类型的语言，java是强类型的.<br><wbr>5、js是非严谨的语言，而java是严谨的.</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr>二、javascript语法：<br><wbr>1、变量：<br><wbr><wbr>通过var关键字定义变量，该变量可以赋予不同类型的常量.<br><wbr><wbr>如：var x=3;<br><wbr><wbr>x="abc";<br><wbr>2、语句<br><wbr><wbr>if,switch(不限定类型),while,do while,for.<br><wbr><wbr>使用逻辑运算符进行布尔表达式连接的时候，使用&amp;&amp;或||。因为在js中非0即为真，0为false.非null为true，null为false.</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>js特有的语句：<br><wbr><wbr>with():可以确定对象所作用的范围，在范围内，可以直接使用对象的属性和行为，而不用对象.属性的方式.</wbr></wbr></wbr></wbr>

<wbr><wbr>for(变量 in 对象)：可以对对象的行为和属性进行遍历.<br><wbr>3、数组.<br><wbr><wbr>对js的数组，特点在于：该数组的长度是可变的，相对于java的集合.<br><wbr><wbr>数组可以存放的元素类型可以是不同的.</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>定义格式：<br><wbr><wbr><wbr>var arr = [3,true,"abc"];<br><wbr><wbr><wbr>var arr = new Array();<br><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr>var arr = [[1,2],["a","b"]];二维数组.<br><wbr><wbr>数组的操作形式和java一样，都是通过for循环进行遍历.<br><wbr>4、函数<br><wbr><wbr>通过关键字function定义函数.<br><wbr><wbr>1,一般函数：<br><wbr><wbr><wbr>格式：<wbr> function 函数名(形式参数, ...)<br><wbr><wbr><wbr><wbr>{<br><wbr><wbr><wbr><wbr><wbr>执行语句;<br><wbr><wbr><wbr><wbr><wbr>return 返回值;<br><wbr><wbr><wbr><wbr>}<br><wbr><wbr>2,动态函数：<br><wbr><wbr><wbr>使用的function对象.<br><wbr><wbr><wbr>例：var show = new Function("x", "y", "return x+y;");<br><wbr><wbr><wbr>特点：可以将参数列表和方法体作为参数传递.</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>3,匿名函数.<br><wbr><wbr><wbr>一般函数的简写形式.<br><wbr><wbr><wbr>function(){};<br><wbr><wbr><wbr>通常可以用于事件的处理.<br><wbr><wbr><wbr>window.onload = function(){alert(onload over)};</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>注意：<br><wbr><wbr><wbr>function show()<br><wbr><wbr><wbr>{<br><wbr><wbr><wbr><wbr>return "show run";<br><wbr><wbr><wbr>}<br><wbr><wbr><wbr>var method = show();<wbr><wbr> ——正确，表示将show方法运行的结果复制给method变量.<br><wbr><wbr><wbr>var method = show;<wbr><wbr><wbr> ——正确，没有括号，表示将show指向对象的地址赋值给method,那么method也指向了该对象，就可以通过method()的形式来调用这个show方法.</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr>三、Js可以通过对象形式将数据进行封装.<br><wbr><wbr>1、首先对对象进行描述，通过函数来完成.<br><wbr><wbr>function Person(name, age)<br><wbr><wbr>{<br><wbr><wbr><wbr>this.name = name;<br><wbr><wbr><wbr>this.age = age;<br><wbr><wbr>}<br><wbr><wbr>var p = new Person("zhangsan", 25);<br><wbr><wbr>alert(p["name"]+".."+p.age);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>p.show = function()<br><wbr><wbr>{<br><wbr><wbr><wbr>alert("show run");<br><wbr><wbr>}<br><wbr><wbr><br><wbr><wbr>2、js中已经定义好的一些对象:String,Math,Date,Globe,Object等等.<br><wbr><wbr><wbr>这些对象都有一个属性：prototype（原型），可以通过该属性获得原对象的引用，然后可以通过该引用给已有的对象赋予新的功能，在使用该对象的时候，就可以直接调用定义好的功能.</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr>例如：将获取数组最大值的自定义功能封装到Array对象中.<br><wbr><wbr><wbr><wbr>function getMax()<br><wbr><wbr><wbr><wbr>{<br><wbr><wbr><wbr><wbr><wbr>var max = 0;<br><wbr><wbr><wbr><wbr><wbr>for (var x = 1; x &lt; this.length; x++)<br><wbr><wbr><wbr><wbr><wbr>{<br><wbr><wbr><wbr><wbr><wbr><wbr>if(this[x] &gt; this[max])<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr>max = x;<br><wbr><wbr><wbr><wbr><wbr>}<br><wbr><wbr><wbr><wbr><wbr>return this[max];<br><wbr><wbr><wbr><wbr>}<br><wbr><wbr><wbr><wbr>Array.prototype.getMax = getMax;<wbr> //给Array对象新增加一个getMax函数。</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr>var arr = [1,5,2,3];<br><wbr><wbr><wbr><wbr>alert("max="+arr.getMax());<br><wbr><wbr>3、常见的全局方法：<br><wbr><wbr><wbr>sarseInt(numstr, [radix]);——可选参数为基数，制定了基数，则将字符串格式的数字按照指定基数转成整数.<br><wbr><wbr><wbr>如：var num = parseInt("110", 2); //结果为6。<br><wbr><wbr><wbr><wbr><wbr><wbr> var num = parseInt("110", 10); //结果为110。</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr>四、javascript和html结合才能被浏览器解释执行.<br><wbr><wbr>结合方式：<br><wbr><wbr>1,通过定义&lt;script&gt;标签将js代码存入其中，并指定type属性.<br><wbr><wbr>2,通过&lt;script&gt;标签，使用src属性连接一个指定的js外部文件.</wbr></wbr></wbr></wbr></wbr></wbr></wbr>