HTML form with multiple hidden control elements of the same name
FormsHidden FieldForms Problem Overview
Is it legal to have an HTML form with more than one "hidden" control element with the same name? I expect to get the values of all of these elements at the server. If it is legal, do the major browsers implement the behavior correctly?
Forms Solutions
Solution 1 - Forms
The browsers are OK with it. However, how the application library parses it may vary.
Programs are supposed to group identically named items together. While the HTML specification doesn't explicitly say this, it is implicitly stated in the documentation on checkboxes:
> Several checkboxes in a form may share > the same control name. Thus, for > example, checkboxes allow users to > select several values for the same > property.
Solution 2 - Forms
Different server-side technologies will vary. With PHP, you can use an array-style syntax for the name to force a collection to be created on the server-end. If posted to the server, $_POST['colors'] will be an array with two values, #003366 and #00FFFF:
<input type="hidden" name="colors[]" value="#003366" />
<input type="hidden" name="colors[]" value="#00FFFF" />
Generally speaking, you'll want to use a standard name without square brackets. Most server-side technologies will be able to parse the resulting data, and provide a collection of some type. Node.js provides helpful functionality via querystring.parse:
const querystring = require('querystring')
querystring.parse('foo=bar&abc=xyz&abc=123') // { foo: 'bar', abc: ['xyz', '123'] }
Solution 3 - Forms
If you have something like this:
<input type="hidden" name="x" value="1" />
<input type="hidden" name="x" value="2" />
<input type="hidden" name="x" value="3" />
Your query string is going to turn out looking like x=1&x=2&x=3... Depending on the server software you are using to parse the query string this might not work well.
Solution 4 - Forms
Yes, and most application servers will collect the matching elements and concatenate them with commas, such that a form like this:
<html>
<form method="get" action="http://myhost.com/myscript/test.asp">
<input type="hidden" name="myHidden" value="1">
<input type="hidden" name="myHidden" value="2">
<input type="hidden" name="myHidden" value="3">
<input type="submit" value="Submit">
</form>
</html>
... would resolve to a URL (in the GET case -- POST would work the same way, though) like this:
> http://myhost.com/myscript.asp?myHidden=1&myHidden=2&myHidden=3
... and would be exposed to you in code like this: (e.g., following something like Response.Write(Request.QueryString("myHidden")):
1, 2, 3
So to grab the values, you'd just split the string and access them as an array (or whatever's comparable in your language of choice).
(Should be clarified: In PHP, it's slightly different (as Johnathan points out, bracket notation exposes the items as an array to your PHP code), but ASP, ASP.NET, and ColdFusion all expose the values as a comma-separated list. So yes, the duplicate naming is completely valid.)
Solution 5 - Forms
HTML5
The non-normative section 4.10.1.3 Configuring a form to communicate with a server explicitly says that it is valid:
> Multiple controls can have the same name; for example, here we give all the checkboxes the same name, and the server distinguishes which checkbox was checked by seeing which values are submitted with that name — like the radio buttons, they are also given unique values with the value attribute.
The normative version of this is simply that it is not forbidden anywhere, and the form submission algorithm says exactly what request should be generated:
- no constraint is violated: https://www.w3.org/TR/html5/forms.html#constraints
- multiple names get added to the "form data set" one after the other: https://www.w3.org/TR/html5/forms.html#constructing-form-data-set
- encodings like
application/x-www-form-urlencodedloop over the "form data set" and spit out multiplekey=valhttps://www.w3.org/TR/html5/forms.html#url-encoded-form-data
Solution 6 - Forms
Specifically for PHP I made some tests with array names in hidden inputs and I share here my results:
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Post Hidden 2D Arrays</title>
</head>
<body>
<form name="formtest" method="POST" target="_self">
<input type="hidden" name="elem['name'][]" value="first">
<input type="hidden" name="elem['name'][]" value="second">
<input type="hidden" name="elem['name'][]" value="third">
<input type="hidden" name="elem['name'][]" value="fourth">
<input type="hidden" name="elem['type'][]" value="normal">
<input type="hidden" name="elem['type'][]" value="classic">
<input type="hidden" name="elem['type'][]" value="regular">
<input type="hidden" name="elem['type'][]" value="basic">
<input type="hidden" name="elem['size'][]" value="4">
<input type="hidden" name="elem['size'][]" value="7">
<input type="hidden" name="elem['size'][]" value="3">
<input type="hidden" name="elem['size'][]" value="6">
<input type="hidden" name="elem['form'][]" value="triangle">
<input type="hidden" name="elem['form'][]" value="square">
<input type="hidden" name="elem['form'][]" value="hexagon">
<input type="hidden" name="elem['form'][]" value="circle">
<input type="submit" name="sendtest" value="Test">
</form>
<xmp>
<?php
print_r($_POST);
?>
</xmp>
</body>
</html>
Submitting the form generates the next result:
Array
(
[elem] => Array
(
['name'] => Array
(
[0] => first
[1] => second
[2] => third
[3] => fourth
)
['type'] => Array
(
[0] => normal
[1] => classic
[2] => regular
[3] => basic
)
['size'] => Array
(
[0] => 4
[1] => 7
[2] => 3
[3] => 6
)
['temp'] => Array
(
[0] => triangle
[1] => square
[2] => hexagon
[3] => circle
)
)
[sendtest] => Test
)
After viewing this result I made more tests looking a better arrange of array values and ended with this (I will show only the new hidden inputs):
<input type="hidden" name="elem[0]['name']" value="first">
<input type="hidden" name="elem[1]['name']" value="second">
<input type="hidden" name="elem[2]['name']" value="third">
<input type="hidden" name="elem[3]['name']" value="fourth">
<input type="hidden" name="elem[0]['type']" value="normal">
<input type="hidden" name="elem[1]['type']" value="classic">
<input type="hidden" name="elem[2]['type']" value="regular">
<input type="hidden" name="elem[3]['type']" value="basic">
<input type="hidden" name="elem[0]['size']" value="4">
<input type="hidden" name="elem[1]['size']" value="7">
<input type="hidden" name="elem[2]['size']" value="3">
<input type="hidden" name="elem[3]['size']" value="6">
<input type="hidden" name="elem[0]['temp']" value="triangle">
<input type="hidden" name="elem[1]['temp']" value="square">
<input type="hidden" name="elem[2]['temp']" value="hexagon">
<input type="hidden" name="elem[3]['temp']" value="circle">
Obtaining this result after submitting form:
Array
(
[elem] => Array
(
[0] => Array
(
['name'] => first
['type'] => normal
['size'] => 4
['temp'] => triangle
)
[1] => Array
(
['name'] => second
['type'] => classic
['size'] => 7
['temp'] => square
)
[2] => Array
(
['name'] => third
['type'] => regular
['size'] => 3
['temp'] => hexagon
)
[3] => Array
(
['name'] => fourth
['type'] => basic
['size'] => 6
['temp'] => circle
)
)
[sendtest] => Test
)
I hope this helps a few.
Solution 7 - Forms
I believe it is legal, at least in cases of radio buttons and check boxes. When I have to dynamically add textbox inputs in XSLT, I give them all the same name; in ASP.NET, Request.Form["whatever_name"] is a string of all these values comma-seperated.
Solution 8 - Forms
I have just tried using the same control name, counties[] for several SELECT inputs so that counties in England, Scotland, Wales and Ireland in each are are all passed as values for the same parameter. PHP handles it fine, but HTML validator gives a warning. I don't know if all browsers would handle this the same way.