JS control select Daquan

1. Check whether item 2 with value = "paravalue" exists in the select option. add an item 3 to the select option. delete an item 4 from the select option. Delete the selected item 5 modify the select option. in value = "paravalue", text is "paratext" 6. Set the first item of text = "paratext" in select to select 7. Set the item of value = "paravalue" in select to select 8. Obtain the value 9 of the selected item in the SELECT statement. Then, the text 10 of the selected item in the SELECT statement is obtained. Then, the index 11 of the selected item in the SELECT statement is cleared. js Code // 1. determine whether the select option contains the item Function jsselectisexititem (objselect, objitemvalue) {var isexit = false; For (VAR I = 0; I <objselect. options. length; I ++) {If (objselect. options [I]. value = objitemvalue) {isexit = true; break;} return isexit;} // 2. add an item Function jsadditemtoselect (objselect, objitemtext, objitemvalue) to the select option {// determine whether there is if (jsselectisexititem (objselect, objitemvalue )) {alert ("the value of this item already exists");} else {var varitem = New Option (objitemtext, objitemvalue); objselect. options. add (varitem); alert ("successfully added") ;}// 3. delete an item Function jsremoveitemfromselect (objselect, objitemvalue) from the select option {// determine whether there is if (jsselectisexititem (objselect, objitemvalue) {for (VAR I = 0; I <objselect. options. length; I ++) {If (objselect. options [I]. value = objitemvalue) {objselect. options. remove (I); break ;}} alert ("deleted successfully") ;}else {alert ("this select does not exist") ;}} // 4. delete the function jsremoveselecteditemfromselect (objselect) {var length = objselect. options. length-1; for (VAR I = length; I> = 0; I --) {If (objselect [I]. selected = true) {objselect. options [I] = NULL ;}}// 5. modify the text of value = "paravalue" in the select option to "paratext" function jsupdateitemtoselect (objselect, objitemtext, objitemvalue) {// determine if (jsselectisexititem (objselect, objitemvalue )) {for (VAR I = 0; I <objselect. options. length; I ++) {If (objselect. options [I]. value = objitemvalue) {objselect. options [I]. TEXT = objitemtext; break ;}} alert ("modified successfully") ;}else {alert ("this select option does not exist") ;}}// 6. set the first item of text = "paratext" in select to the selected function jsselectitembyvalue (objselect, objitemtext) {// determine whether var isexit = false; For (VAR I = 0; I <objselect. options. length; I ++) {If (objselect. options [I]. TEXT = objitemtext) {objselect. options [I]. selected = true; isexit = true; break;} // show the result if (isexit) {alert ("selected successfully ");} else {alert ("this select does not exist") ;}// 7. set item of value = "paravalue" in select to selected document. all. objselect. value = objitemvalue; // 8. obtain the value var currselectvalue = Document of the selected item in the SELECT statement. all. objselect. value; // 9. the text var currselecttext = document. all. objselect. options [document. all. objselect. selectedindex]. text; // 10. the index var currselectindex = document. all. objselect. selectedindex; // 11. clear the select item Document. all. objselect. options. length = 0;