Jscript 5.0中的新特性

 
jscript 5.0中的新特性

jscript 5.0唯一的改变是引入了错误处理。
java风格的try和catch结构在jscript 5.0中得到了支持。例如：

function getsomekindofindexthingy() {

       try {
              // if an exception occurs during the execution of this
              // block of code, processing of this entire block will
              // be aborted and will resume with the first statement in its
              // associated catch block.
              var objsomething = server.createobject (“somecomponent”);
              var intindex = objsomething.getsomeindex();
              return intindex;
       }

       catch (exception) {
              // this code will execute when *any* exception occurs during the
              // execution of this function
              alert (‘oh dear, the object didn’t expect you to do that’);
       }
}

内建的jscript error对象有3个属性，它们定义了上次的运行期错误。可在catch块中使用它们获得有关错误的更多信息。
alert (error.number);              // gives the numeric value of the error number
// and the result with 0xffff to get a ‘normal’ error number in asp

alert (error.description);          // gives an error desciption as a string
假如你想招抛出自己的错误，可用一个定制的异常对象引发一个错误（或异常）。然而，由于没有内建的异常对象，必须自己定义一个结构：
// define our own exception object
function myexception (intnumber, strdescripton, strinfo) {
       this.number = intnumber;            // set the number property
       this.description = strdescription;       // set the description property
       this.custominfo = strinfo;          // set some ‘information’ property
}
这样的对象可用来在页面中引发定制的异常。这通过使用throw关键字，然后检查catch块中的异常类型来实现：
function getsomekindofindexthingy() {
       try {
              var objsomething = server.createobject (“somecomponent”);
              var intindex = objsomething.getsomeindex();
              if (intindex == 0) {
                     // create a new myexception object
                     theexception = new myexception (0x6f1, “zero index not permitted”,
                                                                             “index_err”);
                     throw theexception;
              }

              catch (objexception) {
                     if (objexception instanceof myexception) {
                            // this is one of our custom exption objects
                            if (objexception.category == “index_err”) {
                                   alert (‘index error: ‘ + objexception.description);
                            else
                                   alert (‘undefined custom error: ‘ + objexception.description);
                            }
                     else
                            // not “our” exception, so display it and raise to next higher routine
                            alert (error.description + ‘ (‘ + error.number + ‘)’);
                            throw exception;
                     }
              }
       }