js学习第一天：基本语法

<script type="text/javascript">
        //变量声明全局
        var temp;
        var tmp2, tmp2 = 3;
        
        function abc() {
            alert(tmp2);
            alert(a);//erro
            //局部变量
            var b = null;
            var a;
            alert(b); //undefined
            alert(b == a);//true 值等于
            alert(b === a);//false 严格等于

            var c = 2.0;
            alert((c.toString()).prototype)
            alert(parseInt(c));//转换为Int类型
            alert(parseInt("dfs123"));//截取 erro
            alert(parseFloat('123abc'));//123
            alert(parseFloat("0xA"));//0
            alert(parseFloat("43.445.55"));//43.445

            alert("abc".substring(1));//abc1
            alert("abc".toUpperCase());//ABC
            alert(123+'a' + c);//123a2.0
            alert("abc".length);

            var arr = "a-b-c".split("-");//[a,b,c]
            for (var i = 0; i < arr.length; i++) {
                alert(arr[i]);
            }
            alert("abc".search("b"));//1 坐标

            //reg 正则表达式
            var str = 'panguan- aidsjf-asdkjfh'
            //方法一 /xxx/
            var reg = /panguan/;
            alert(reg.exec(str));//查找
            alert(reg.test(str));//判断
            //方法2  //new一个reg对象
            var reg = new RegExp('panguan');
            alert(reg.exec(str));

            //array
            var arr = [1,2,3,'abc',false];//任何类型
            alert(arr);
            var arr1 = new Array();
            arr1[1] = 'abc'; //赋值
            alert(arr1);
            alert(arr1.length);
            alert(arr1[0]);//undefined
            alert(typeof(arr));

            //运算符
            5>2?alert(false):alert((true));
            var a,b,c;
            a = (b=5,c=2,d=3);
            alert(a)//取最右边的
            var e,f,g;
            a = void(e=3,f=5,g=9);
            alert(a);//a = undefined
            alert(typeof(a));
            alert(typeof(e));
            var  arr = [1,2,3];
            alert(arr instanceof Array);

            //其他的特殊语句
            with(document){
                write("第一句<br/>");
                write("第二句<br/>");
                write("第三句<br/>");
            }
            //try-cath
            try{
                if (c) {
                    throw new Error("错误呢");
                }
            }catch(e){
                //TODO handle the exception
                document.write(e.message + '<br/>')
            }finally{
                document.write("finally");
            }
        }

        function abc(){
            a; // a is not defined
            alert(a);
        }
    </script>