js code to get server control value_javascript skills

1. Get the value and text of the selected item in the drop-down list (select)
The code select.htm example is as follows:

2. Get the radio button (radio) group Value and modify the selected item
I saw many posts saying that js can directly use document.getElementById("oper").value to get the value of the radio button group, although it is the same as the radio button group. The drop-down list (also an array of list items) is also an array. In this way, you can get the value of the drop-down list, but the radio button group cannot get the selected value. After careful study, the summary is as follows:
Unlike the drop-down list, the radio button must use this.form.oper or document.getElementsByName('oper') to obtain the array object. document.getElementById('oper') cannot Get the array object (select can). Moreover, the value must be obtained through a loop judgment, and .value cannot be used directly (select can be used). To change the selected item of the radio button group, you must also use loop judgment to change the value of each radio button.
The test code radio.html is as follows: