JQuery implements three control methods (drop-down, single-choice, and check)

Radion <input type = "radio" name = "rd" id = "rd1" checked = "checked" value = "rd1"/> <input type = "radio" name =" rd "id =" rd2 "value =" rd2 "/> <input type =" radio "name =" rd "id =" rd3 "value =" rd3 "/> 1. to obtain the selected value, you can: $ ('input: radio: checked '). val (); $ ("input [type = 'Radio ']: checked "). val (); $ ("input [name = 'rd']: checked "). val (); 2. set the first Radio to the selected value: $ ('input: radio: first '). attr ('checked', 'checked'); or $ ('input: radio: first '). attr ('checked', 'true'); Note: attr ("checked", 'checked') = attr ("checked", 'true ') = attr ("checked", true) 3. set the last Radio to the selected value: $ ('input: radio: lay '). attr ('checked', 'checked'); or $ ('input: radio: lae '). attr ('checked', 'true'); 4. set any radio as the selected value based on the index value: $ ('input: radio '). eq (index value ). attr ('checked', 'true'); index value = 0, 1, 2 .... or $ ('input: radio '). slice (1, 2 ). attr ('checked', 'true'); 5. set Radio as the selected Value based on the value $ ("input: radio [Value = 'rd2 ']"). attr ('checked', 'true'); or $ ("input [value = 'rd2 ']"). attr ('checked', 'true'); 6. delete Radio $ ("input: radio [Value = 'rd2 ']") whose value is rd2. remove (); 7. delete the number of Radio $ ("input: radio "). eq (index value ). remove (); index value = 0, 1, 2 .... for example, delete 3rd Radio: $ ("input: radio "). eq (2 ). remove (); 8. traverse Radio $ ('input: radio '). each (function (index, domEle) {// write code }); dropDownList <select id = "sel"> <option value = "1" selected = "selected"> a </option> <option value = "2"> B </option> <option value = "3"> c </option> <option value = "4"> d </option> <option value = "5"> e </option> </select> 1. obtain the Value of the selected item: $ ('select # sel option: selected '). val (); or $ ('select # sel '). find ('option: selected '). val (); get the Text value of the selected item: $ ('select # seloption: selected '). text (); or $ ('select # sel '). find ('option: selected '). text (); 2. obtain the index value of the selected item: $ ('select # sel '). get (0 ). selectedIndex; 3. obtain the maximum index value of the current option: $ ('select # sel option: la '). attr ("index") 4. get the DropdownList length: $ ('select # sel ') [0]. options. length; or $ ('select # sel '). get (0 ). options. length; 5. set the first option to the selected value: $ ('select # sel option: first '). attr ('selected', 'true') or $ ('select # sel ') [0]. selectedIndex = 0; 6. set the last option to the selected value: $ ('select # sel option: last ). attr ('selected', 'true') 7. set any option to the selected value based on the index value: $ ('select # sel ') [0]. selectedIndex = index value; index value = 0, 1, 2 .... 8. set option of Value = 4 to the selected Value: $ ('select # sel '). attr ('value', '4'); or $ ("select # sel option [value = '4']"). attr ('selected', 'true'); 9. delete option: $ ("select # sel option [Value = '3']") for value = 3. remove (); 10. delete the number of options: $ ("select # sel option "). eq (index value ). remove (); index value = 0, 1, 2 .... for example, delete 3rd Radio: $ ("select # sel option "). eq (2 ). remove (); 11. delete the first option: $ ("select # sel option "). eq (0 ). remove (); or $ ("select # sel option: first "). remove (); 12. delete the last option: $ ("select # sel option: last "). remove (); 13. delete dropdownlist: $ ("select # sel "). remove (); 14. add an option: $ ("select # sel") After select "). append ("<option value = '6'> f </option>"); 15. add an option: $ ("select # sel") before select "). prepend ("<option value = '0'> 0 </option>"); 16. traverse option: $ ('select # sel option '). each (function (index, domEle) {// write code }); checkBox <input type = "checkbox" id = "ck1" name = "ck" vlaue = "1" checked = "checked"/> <input type = "checkbox" id =" ck2 "name =" ck "vlaue =" 2 "/> <input type =" checkbox "id =" ck3 "name =" ck "vlaue =" 3 "/> <input type = "checkbox" id = "ck4" name = "ck" vlaue = "4"/> 1. get a single checkbox selected item (three methods): $ ("input: checkbox: checked "). val () or $ ("input: [type = 'checkbox']: checked "). val (); or $ ("input: [name = 'ck ']: checked "). val (); 2. obtain multiple checkbox selected items: $ ('input: checkbox '). each (function () {if ($ (this ). attr ('checked') = true) {alert ($ (this ). val () ;}}); 3. set the first checkbox to the selected value: $ ('input: checkbox: first '). attr ("checked", 'checked'); or $ ('input: checkbox '). eq (0 ). attr ("checked", 'true'); 4. set the last checkbox to the selected value: $ ('input: radio: lay '). attr ('checked', 'checked'); or $ ('input: radio: lae '). attr ('checked', 'true'); 5. set any checkbox as the selected value based on the index value: $ ('input: checkbox ). eq (index value ). attr ('checked', 'true'); index value = 0, 1, 2 .... or $ ('input: radio '). slice (1, 2 ). attr ('checked', 'true'); 6. multiple checkboxes are selected: 1st and 2nd checkboxes are selected at the same time: $ ('input: radio '). slice (0, 2 ). attr ('checked', 'true'); 7. set checkbox as the selected Value based on the value: $ ("input: checkbox [Value = '1']"). attr ('checked', 'true'); 8. delete the checkbox: $ ("input: checkbox [Value = '1']") with value = 1. remove (); 9. delete the number of checkpoints: $ ("input: checkbox "). eq (index value ). remove (); index value = 0, 1, 2 .... for example, delete 3rd checkboxes: $ ("input: checkbox "). eq (2 ). remove (); 10. traverse checkbox: $ ('input: checkbox '). each (function (index, domEle) {// write code}); 11. select all $ ('input: checkbox '). each (function () {$ (this ). attr ('checked', true) ;}); 12. unselect all: $ ('input: checkbox '). each (function () {$ (this ). attr ('checked', false );});