The use of select in JS and jquery

1.jsvar Obj=document.getelementbyid (selectid); obj.options.length = 0; Clear all content obj.options[index] = new Option ("three", 3);  Change the corresponding value obj.options[index].selected = true;  Keep selected Obj.add (New Option ("4", "4")); "Text", "value" var index = obj.selectedindex;obj.options.remove (index);//Delete the selected item 2.jquery$ ("#select_id"). Append ("<option Value= ' Value ' >Text</option> ');  Append an option (drop-down) $ ("#select_id") to the Select. Find (' option:selected '). Text (); Gets the Select selected text$ ("#select_id"). Val (); Gets the Select selected value$ ("#select_id option[index= ' 0"). Remove ();//delete the option$ with an index value of 0 ("#select_id option[value= ' 3 ']"). Remove (); Remove option$ ("#select_id option[text= ' 4") with a value of 3. Remove (); Delete the option$ ("#mselect_id") with a text value of 4. Change (function () {     //Add the action code needed to execute})

　　

The use of select in JS and jquery