Create a cascading drop-down list box from a JavaScript script __java

This module uses JavaScript technology to determine whether the search condition is empty and to change the data in the corresponding list based on the data selected by the user. When the user selects a search condition in the first list, the data in the second list changes and corresponds to the data in the first list, with the following key code:

Code location: Supporting Resources \mr\01\select.php

01  <script>  02  function fetch () {                //determines whether the search keyword is empty   03       if (form1.key.value== "") {  04          alert (" Please enter a search keyword. ");   05          form1.value.select ();   06          return false;   07      }   08           return true;   09&NBSP;&NBSP}   10  </script>  11  <script language= " JavaScript ">  12  function press (opt) {             //defines the press () method, controls the Select2 display value   13  //opt for the Drop-down list box to indicate the number of existing options   14      &nbsP;form1.select2.options[opt]=new option (ok= (form1.select2.options[opt))?   15       form1.select2.options[opt].innertext+string.fromcharcode (Event.keycode):   16       string.fromcharcode (Event.keycode), OK)   17       form1.select2.selectedindex=opt;   18&NBSP;&NBSP}   19  </script>  20  <script language= " JavaScript ">  21  function up (opt) {            //defines the up () method to control Select2 value   22&NBSP;&NBSP;//OPT indicates the number of existing options   23       if (Form1.select2.options[opt]) {  24           if (event.keycode==8) {  25               var str=form1.select2.options[opt].innerText;   26&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&Nbsp;        var len=str.length;   27               Form1.select2.options[opt].innertext=str.substring (0,len-1);   28              if ( form1.select2.options[opt].innertext== " ") Select2.remove (2);   29          }   30           if (event.keycode==32) {  31               form1.select2.options[opt].innertext+= " ";   32          }   33       }   34  }   35  </script>