jquery Gets the code for the input form value

jquery take radio radio button values
$ ("input[name= ' Items ']:checked"). Val ();
jquery Radio value, checkbox value, select Value, Radio selected, CheckBox selected, select selected, and its related
gets the value of a set of radio selected items
var item = $ (' input[name=items][checked] '). Val ();
gets the text of the Select selected item
var item = $ ("Select[name=items] option[selected]"). Text ();
the second element of the Select drop-down box is the currently selected value
$ (' #select_id ') [0].selectedindex = 1;
Radio The second element of a radio group is the currently selected value
$ (' input[name=items] '). Get (1). checked = true;

Get Value:

text box, text area: $ ("#txt"). attr ("value");
Multi Box checkbox:$ ("#checkbox_id"). attr ("value");
Radio Group Radio: $ ("input[type=radio][checked]"). Val ();
Drop- down box select: $ (' #sel '). Val ();

Control form elements:
text box, text area: $ ("#txt"). attr ("Value", "");//Clear Contents
$ ("#txt"). attr ("value", ' 11 ');//fill content

multiple Marquee checkbox: $ ("#chk1"). attr ("Checked", "");//No tick
$ ("#chk2"). attr ("Checked", true);//Tick
if ($ ("#chk1"). attr (' checked ') ==undefined)//Determine if a tick has been made

Radio Group Radio: $ ("Input[type=radio]"). attr ("Checked", ' 2 ');//Set value=2 for the currently selected item
Drop- down box select: $ ("#sel"). attr ("value", '-sel3 ');//Set the VALUE=-SEL3 item as the current selection
$ ("<option value= ' 1 ' >1111</option><option value= ' 2 ' >2222</option>"). AppendTo ("#sel") option to add a drop-down box
$ ("#sel"). empty ();//Empty drop-down box

just started to touch jquery, a lot of things are unfamiliar
When you use $ ("#id") to get the input element of the page, you find $ ("#id"). Value cannot be obtained

then finally, with the help of the great Baidu, I found the reason for the problem:
$ ("") is a jquery object, not a DOM element

value is a property of the DOM element

jquery corresponds to the Val

Val (): Gets the current value of the first matching element.

Val (val): Sets the value of each matching element.

so the code should write this:

Value: val = $ ("#id") [0].value;
Assignment Value:
$ ("#id") [0].value = "new value";
or $ ("#id"). Val ("new value");

or it can be: val = $ ("#id"). attr ("value");

jquery Gets the code for the input form value