var str="1、从以下URL中http://www.baidu.com/about/news.php 中将.php给截取出来";
document.write(str.substr(str.lastIndexOf("."),4));

2、将以下字符串javascript翻转过来   --?不允许使用reverse()方法  tpircsavaj  11期
var str="javascript";
for (var i = str.length-1; i>=0; i--) {
    document.write(str[i]);
};

var str="javascript";
for (var i = str.length-1; i>=0; i--) {
    document.write(str[i]);
};

var die      = new Date();
var now      = die.getTime();
var formerly = new Date("1992-08-06").getTime();
var day      = ((now-formerly)/1000/60/60/24);
document.write("现在一共活了"+Math.ceil(day)+"天");

var str="a?sh>n";
var str_len=str.length;
function checkUser(userName){
    var arr=["*","%","&","<",">","!","@","#"];
    //获取数组的长度
    var arr_len=arr.length;
    //用户名字符串
    for (var i = 0; i < str_len; i++) { 
        for (var j = 0; j< arr_len; j++) { 
            if(str[i]==arr[j]){
            return false;
            }
        }    
    }
    return true;
} 
if(checkUser(str)){
    document.write("用户名合法");
}else{
    document.write("用户名非法");
}  

  var myDate = new Date();
  var y = myDate.getFullYear();
  var m = zero(myDate.getMonth()+1);
  var d = zero(myDate.getDate());
  var h = zero(myDate.getHours());

  var arr = [‘星期天‘,‘星期一‘,‘星期二‘,‘星期三‘,‘星期四‘,‘星期五‘,‘星期六‘];

  var str="<h2>输出当前的系统时间日期</h2>";
      str+="今年是："+y+"年";
      str+="<br>本月是"+m;
      str+="<br>今天是"+d;
      str+="<br>现在是"+h+"时";
         //info.innerHTML=str;
         document.write(str); 

  //前导零
  function zero(i){
      if(i<10){return "0"+i;}else{return i;}
  }

 var str = "北京传智教育，是一家专业培训的教育机构";
  var reg = /教育/gi;
  document.write(str.replace(reg,"education"));