Do checkbox inputs only post data if they re checked

Question

Is it standard behaviour for browsers to only send the checkbox input value data if it is checked upon form submission   And if no value data is supplied  is the default value always  on    Assuming the above is correct  is this consistent behaviour across all browsers

User · Answer

I have a page  form  that dynamically generates checkbox so these answers have been a great help    My solution is very similar to many here but I can t help thinking it is easier to implement   First I put a hidden input box in line with my checkbox   i e     lt td gt  lt input class    chkhide  type  hidden  name  delete milestone    value  off   gt  lt input type  checkbox  name  delete milestone      class  chk milestone   gt  lt  td gt    Now if all the checkboxes are un-selected then values returned by the hidden field will all be off        For example  here with five dynamically inserted checkboxes  the form POSTS the following values      delete milestone    gt   array  size 7    0   gt  string  off   length 3    1   gt  string  off   length 3    2   gt  string  off   length 3    3   gt  string  on   length 2    4   gt  string  off   length 3    5   gt  string  on   length 2    6   gt  string  off   length 3    This shows that only the 3rd and 4th checkboxes are  on or checked     In essence the dummy or hidden input field just indicates that everything is off unless there is an  on  below the off index  which then gives you the index you need without a single line of client side code

User · Answer

Is it standard behaviour for browsers to only send the checkbox input   value data if it is checked upon form submission    Yes  because otherwise there d be no solid way of determining if the checkbox was actually checked or not  if it changed the value  the case may exist when your desired value if it were checked would be the same as the one that it was swapped to       And if no value data is supplied  is the default value always  on     Other answers confirm that  on  is the default  However  if you are not interested in the value  just use   if  isset   POST  the checkbox             name  the checkbox  is checked

User · Answer

Having the same problem with unchecked checkboxes that will not be send on forms submit  I came out with a another solution than mirror the checkbox items   Getting all unchecked checkboxes with  var checkboxQueryString    form find   input type   checkbox    not     checked       each function  i  e       checkboxQueryString      amp        e   attr   name        N

User · Answer

Checkboxes are posting value  on  if and only if the checkbox is checked  Insted of catching checkbox value you can use hidden inputs  JS   var chk      input type  checkbox          chk each function            var v     this  attr  checked       checked  1 0            this  after   lt input type  hidden  name      this  attr  rel      value    v      gt              chk change function             var v     this  is   checked   1 0            this  next  input type  hidden     val v             HTML    lt label gt Active lt  label gt  lt input rel  active  type  checkbox    gt

User · Answer

I resolved the problem with this code   HTML Form   lt input type  checkbox  id  is-business  name  is-business  value  off  onclick  changeValueCheckbox this    gt   lt label for  is-business  gt Soy empresa lt  label gt    and the javascript function by change the checkbox value form     change value of checkbox element function changeValueCheckbox element      if element checked       element value  on      else      element value  off           and the server checked if the data post is  on  or  off   I used playframework java          final Map lt String  String   gt  data   request   body   asFormUrlEncoded             if  data get  is-business   0  equals  on                  login setType new MasterValue Login BUSINESS TYPE              else               login setType new MasterValue Login USER TYPE

User · Answer

Yes  standard behaviour is the value is only sent if the checkbox is checked  This typically means you need to have a way of remembering what checkboxes you are expecting on the server side since not all the data comes back from the form   The default value is always  on   this should be consistent across browsers    This is covered in the W3C HTML 4 recommendation      Checkboxes  and radio buttons  are on off switches that may be toggled   by the user  A switch is  on  when the control element s checked   attribute is set  When a form is submitted  only  on  checkbox   controls can become successful

User · Answer

input type  hidden  name  is main  value  0   input type  checkbox  name  is main  value  1   so you can control like this as I did in the application  if it checks then send value 1 otherwise 0

User · Answer

If checkbox isn t checked then it doesn t contribute to the data sent on form submission  HTML5 section 4 10 22 4 Constructing the form data set describes the way form data is constructed   If any of the following conditions are met  then skip these substeps for this element        The field element is an input element whose type attribute is in the Checkbox state and whose checkedness is false   and then the default valued on is specified if value is missing   Otherwise  if the field element is an input element whose type attribute is in the Checkbox state or the Radio Button state  then run these further nested substeps  If the field element has a value attribute specified  then let value be the value of that attribute  otherwise  let value be the string  quot on quot    Thus unchecked checkboxes are skipped during form data construction  Similar behavior is required under HTML4  It s reasonable to expect this behavior from all compliant browsers

User · Answer

None of the above answers satisfied me  I found the best solution is to include a hidden input before each checkbox input with the same name     lt input type  hidden  name  foo    value  off   gt    lt input type  checkbox  name  foo     gt   Then on the server side  using a little algorithm you can get something more like HTML should provide   function checkboxHack array  checkbox input   array        foo           foreach  checkbox input as  value            if  value      on                 array pop  foo                      foo      value            return  foo      This will be the raw input  array       0   gt   off       1   gt   on       2   gt   off       3   gt   off       4   gt   on       5   gt   off       6   gt   on        And the function will return  array       0   gt   on       1   gt   off       2   gt   on       3   gt   on

User · Answer

From HTML 4 spec  which should be consistent across almost all browsers   http   www w3 org TR html401 interact forms html checkbox     Checkboxes  and radio buttons  are on off switches that may be toggled   by the user  A switch is  on  when the control element s checked   attribute is set  When a form is submitted  only  on  checkbox   controls can become successful    Successful is defined as follows      A successful control is  valid  for submission  Every successful   control has its control name paired with its current value as part of   the submitted form data set  A successful control must be defined   within a FORM element and must have a control name

User · Answer

In HTML  each  lt input   gt  element is associated with a single  but not unique  name and value pair  This pair is sent in the subsequent request  in this case  a POST request body  only if the  lt input   gt  is  successful    So if you have these inputs in your  lt form gt  DOM    lt input type  text      name  one    value  foo                           gt   lt input type  text      name  two    value  bar     disabled  disabled    gt   lt input type  text      name  three  value  first                         gt   lt input type  text      name  three  value  second                        gt    lt input type  checkbox  name  four   value  baz                           gt   lt input type  checkbox  name  five   value  baz     checked  checked      gt   lt input type  checkbox  name  six    value  qux     checked  checked  disabled  disabled    gt   lt input type  checkbox  name         value  seven   checked  checked      gt    lt input type  radio     name  eight  value  corge                         gt   lt input type  radio     name  eight  value  grault  checked  checked      gt   lt input type  radio     name  eight  value  garply                        gt    Will generate these name value pairs which will be submitted to the server   one foo three first three second five baz eight grault   Notice that    two and six were excluded because they had the disabled attribute set  three was sent twice because it had two valid inputs with the same name  four was not sent because it is a checkbox that was not checked six was not sent despite being checked because the disabled attribute has a higher precedence  seven does not have a name    attribute sent  so it is not submitted    With respect to your question  you can see that a checkbox that is not checked will therefore not have its name value pair sent to the server - but other inputs that share the same name will be sent with it   Frameworks like ASP NET MVC work around this by  surreptitiously  pairing every checkbox input with a hidden input in the rendered HTML  like so    Html CheckBoxFor  m   gt  m SomeBooleanProperty     Renders    lt input type  checkbox  name  SomeBooleanProperty  value  true    gt   lt input type  hidden    name  SomeBooleanProperty  value  false    gt    If the user does not check the checkbox  then the following will be sent to the server   SomeBooleanProperty false   If the user does check the checkbox  then both will be sent   SomeBooleanProperty true SomeBooleanProperty false   But the server will ignore the  false version because it sees the  true version  and so if it does not see  true it can determine that the checkbox was rendered and that the user did not check it - as opposed to the SomeBooleanProperty inputs not being rendered at all

User · Answer

Just like ASP NET variant  except put the hidden input with the same name before the actual checkbox  of the same name   Only last values will be sent  This way if a box is checked then its name and value  on  is sent  whereas if it s unchecked then the name of the corresponding hidden input and whatever value you might like to give it will be sent  In the end you will get the   POST array to read  with all checked and unchecked elements in it   on  and  false  values  no duplicate keys  Easy to process in PHP

[html] Do checkbox inputs only post data if they're checked?

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