PHP check if it is a valid HTML attribute

Question

I would like to check if a given string could be a valid HTML attribute. If this isn't the case, I will add that string with a prefix of data- to the element. How would I go about this?

For example when the user wants to add a attribute, it passes it to the $attributes array like this:

    $attr = '';
    foreach ( $attributes as $key => $value ) {
        if (is_attr($key)) {
            $attr .= $key . '="' . $value . '" ';
        } else {
            $attr .= 'data-' . $key . '="' . $value . '" ';
        }
    }

So this will finally be added to a form element like an input or textarea or something like that.

... how would the implementation of is_attr($key) look like?

Update: I was hoping I could create the attribute with the DomDocument() class and then validate it to see if the attribute is officially supported. No luck so far.

You can take a look at this answer (there's a nice regex in the comments too), also at this MDN list, but note that le list might change with new specifications. Note also that you can set any attribute to an element if characters are valid, even if not used natively as a tag parameter, the attribute will be there. — Kaddath
– Kaddath, Commented Apr 30, 2019 at 7:35
"how would the implementation of is_attr($key) look like?" — It would need to take more than one attribute for a start. HTML rules include things like "An input element may have a multiple attribute but only if it has type="file". HTML validation is complicated … too complicated to write a complete solution to in a stackoverflow answer. (Voting to close as too broad). — Quentin
– Quentin, Commented Apr 30, 2019 at 8:35

Rahul · Accepted Answer · 2019-04-30 09:00:56Z

1

Here is is_attr function to check valid attributes of input or textarea.

function is_attr($attr, $elementType)
{
    $input       = ["autocomplete", "autofocus", "disabled", "list", "name", "readonly", "required", "tabindex", "type", "value"];
    $globalAttrs = ["accesskey", "class", "contenteditable", "contextmenu", "dir", "draggable", "dropzone", "id", "lang", "style", "tabindex", "title", "inputmode", "is", "itemid", "itemprop", "itemref", "itemscope", "itemtype", "lang", "slot", "spellcheck", "translate"];
    $select      = ["autofocus", "disabled", "form", "multiple", "name", "required", "size"];
    $textarea    = ["autocapitalize", "autocomplete", "autofocus", "cols", "disabled", "form", "maxlength", "minlength", "name", "placeholder", "readonly", "required", "rows", "spellcheck", "wrap"];
    return (in_array($attr, $globalAttrs) || in_array($attr, $$elementType));
}
echo is_attr('accesskey','select');

I have taken all the valid attributes from official html doc.

edited Apr 30, 2019 at 9:00

answered Apr 30, 2019 at 7:33

Rahul

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9 Comments

04FS Over a year ago

Not all of those are valid on input and textarea …

Quentin Over a year ago

"I have taken all the valid attributes from official html doc." — the document you link to is not remotely "official"

Quentin Over a year ago

You missed out data-*, and id, class (probably some other stuff too, but they jumped out at me).

Quentin Over a year ago

re edit: data-* is still missing, the document you link to still isn't an official one, and you missed out a bunch of attributes which are conditionally allowed on an input element.

Rahul Over a year ago

Hello @Quentin sir, I saw that in documentation, but that's special case of OP. He wants to replace attributes which are not valid with data-, that's why, I didn't included that in my arrays. I hope you get my concern.

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