Javascript is a drop-down list of provincial/municipal connections.

Javascript is a drop-down list of provincial/municipal connections.
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Object. options. add (new Option (label, value) method to add an option object to the Set; The object. options. remove (index) method removes the specified items in the options set; Object. options (index) or options. item (index) can be used to obtain the specified items in the options set through the index; The select tag also has an attribute selectedIndex, which may be used to obtain the selected option index: object. selectedIndex // 1. clear the options set function optionsClear (object) {var length = object. options. length; for (var I = length-1; I> = 0; I --) {e. options. remove (I) ;}// 2. add a new optionfunction addOption (object) {object. add (new Option (label, value); // use the last item in the options set to obtain the focus object. selectedIndex = object. lentht-1;} // 3. delete the specified optionfunction removeOption (index) {if (index> = 0) {object. remove (index); // use the last item in the options set to obtain the focus object. selec TedIndex = object. lentht-1;} // 4. obtain the real value of the currently selected option valuefunction getCurrentOptionValue (index) {if (index> = 0) return object (index ). value;} // 5. obtain the display value of the currently selected option labelfunction getCurrentOptionLabel (index) {if (index> = 0) return object (index ). text;} // The following is the date linkage drop-down box: function YYYYMMDD () {// set the month set MonHead = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]; // clear all content in the year drop-down box, including spaces var yObj = document. form1.yearopti OnsClear (yObj); // assign the content yObj to the year drop-down box. options. add (new Option ("select", 0); for (var I = 1950; I <= new Date (). getFullYear (); I ++) // The document ended this year based on January 1, 1950. form1.year. options. add (new Option (I, I); // clear all content in the month drop-down box, mainly including spaces var mObj = document. form1.month; optionsClear (mObj); // the drop-down list of the month to be assigned. form1.month. options. add (new Option ("select", 0); for (var I = 1; I <13; I ++) document. form1.month. options. add (new Option (I, I) ); // Specify the initial value of the year document. form1.year. value = document. getElementsByName ("YYYY") [0]. value; // specifies the initial value of the month document. form1.month. value = document. getElementsByName ("MM") [0]. value; // assign a date to the var n = MonHead [document. form1.month. value-1]; if (document. form1.month. value = 2 & IsPinYear (YYYYvalue) n ++; writeDay (n); // the initial value of the date assigned to the document. form1.date. value = document. getElementsByName ("DD") [0]. value;} // Date changes when the year changes (mainly to determine the year of the week) fun Ction YYYYDD (str) {var MMvalue = document. form1.month. options [document. form1.month. selectedIndex]. value; if (MMvalue = "") {var e = document. form1.date; optionsClear (e); return;} var n = MonHead [MMvalue-1]; if (MMvalue = 2 & IsPinYear (str) n ++; writeDay (n)} // The date linkage function MMDD (str) {var YYYYvalue = document. form1.year. options [document. form1.year. selectedIndex]. value; if (YYYYvalue = "") {var e = Document. form1.date; optionsClear (e); return;} var n = MonHead [str-1]; if (str = 2 & IsPinYear (YYYYvalue) n ++; writeDay (n)} // function writeDay (n) {var e = document. form1.date; optionsClear (e); for (var I = 1; I <(n + 1); I ++) e. options. add (new Option (I, I);} // determines whether the function IsPinYear (year) {return (0 = year % 4 & (year0! = 0 | year @ 0 = 0);} // clear all content in the drop-down box function optionsClear (e) {var length = object. options. length; for (var I = length-1; I> = 0; I --) {e. options. remove (I );}} More benefits // 1 check whether any selected if (objSelect. selectedIndex>-1) {// indicates selected} else {// indicates not selected} // 2 Delete the selected item objSelect. options [objSelect. selectedIndex] = null; // 3 add item objSelect. options [objSelect. length] = new Option ("hello", "hello"); // 4 modify the selected item objSelect. options [objSelect. selectedIndex] = new Option ("hello", "hello"); // 5 get the selected text objSelect. options [objSelect. selectedIndex]. text; // 6 get the value of the selected item objSelect. options [objSelect. selectedIndex]. value;