Code for jquery to obtain the input form value _ jquery

At the beginning, I started to get familiar with jquery and collect and organize some form operations. Jquery returns the value of the radio button.
$ ("Input [name = 'items ']: checked"). val ();
Jquery radio, checkbox, select, radio, checkbox, select, and related
Obtains the value of a set of radio selected items.
Var item = $ ('input [name = items] [checked] '). val ();
Obtain the text of the selected select item.
Var item = $ ("select [name = items] option [selected]"). text ();
The second element in the select drop-down box is the selected value.
$ ('# Select_id') [0]. selectedIndex = 1;
The second element of the radio Group is the currently selected value.
$ ('Input [name = items] '). get (1). checked = true;

Get value:

Text Box, text area: $ ("# txt"). attr ("value ");
Multiple choice 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 the content
$ ("# Txt"). attr ("value", '11'); // fill in the content

Multiple choice box checkbox: $ ("# chk1"). attr ("checked", ''); // do not check
$ ("# Chk2"). attr ("checked", true); // check
If ($ ("# chk1"). attr ('checked') = undefined) // you can check whether the checked has been checked.

Radio Group radio: $ ("input [type = radio]"). attr ("checked", '2'); // set the project with value = 2 as the currently selected item
Drop-down box select: $ ("# sel"). attr ("value", '-sel3'); // set the value =-sel3 project to the currently selected item
$ (" 1111 2222"). AppendTo (" # sel ") // Add the option in the drop-down box
$ ("# Sel"). empty (); // clear the drop-down list

I was just getting started with jquery and was unfamiliar with many things.
When $ ("# id") is used to obtain the page input element, it is found that $ ("# id"). value cannot get the value.

Finally, with the help of the great Baidu, I found the cause of the problem:
$ ("") Is a jquery object, not a dom element

Value is the attribute of dom element.

Jquery corresponds to val.

Val (): obtains the current value of the First Matching Element.

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

Therefore, the code should be written as follows:

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

Alternatively, you can: val = $ ("# id"). attr ("value ");