Thymeleaf - Add attribute without value

Question

In Thymeleaf I would like to generate following HTML

<span data-my-attr>
</span>

I would like to display data-my-attr conditionally, but there seems to be no way how to display or NOT to display an empty attribute conditionally.

In case of required attribute there is th:required but for custom attributes there is nothing.

I tried to use th:attr="'data-my-attr'=${value}" and value is true or false, but it does not work.

jmmygoggle · Accepted Answer · 2024-11-19 13:54:53Z

3

Let's assume condition is true when your attribute should be shown and false when it shouldn't. You can have following:

<span data-my-attr th:attr="${condition} ? 'meaningless' : 'data-my-attr'=''"></span>

Explanation:

According to this thread when you specify the empty value for an attribute within th:attr then Thymeleaf will delete this attribute. So in above snippet:

data-my-attr is added by default.
The empty value is assigned to an attribute using th:attr.
The name of the attribute overriden with empty value is selected accordingly to ${condition}.
When ${condition} is true then data-my-attr should stay so any meaningless name (not present within the tag) should be picked.
Otherwise data-my-attr should be deleted so this name is picked.

Feels hacky but such a way of attribute removal seems working since 2012. Therefore I'd consider it stable.

edited Nov 19, 2024 at 13:54

jmmygoggle

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answered Nov 13, 2020 at 1:10

Jakub Ch.

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6 Comments

michal.jakubeczy Over a year ago

thanks, your solution works. It's a hacky and 'hard-to-read' one, but I think we don't have anything better in Thymeleaf.

Jakub Ch. Over a year ago

@michal.jakubeczy Another way I thought of is

<th:block th:if="{$condition}"><span data-my-attr></span></th:block><th:block th:unless="${condition}"><span></span></th:block>

. Less hacky but more verbose.

michal.jakubeczy Over a year ago

yes, sure that is an option too. But disadvantage is a lot of code duplicity. I was wondering why [(${expression ? 'data-my-attribute' : ''})] inside element is not working. That would be a great way to do it.

Jakub Ch. Over a year ago

I think code duplicity can be avoided by using th:fragment. But sure, an expression you've mentioned would be an advantage. It might be a good idea to raise an issue in Thymeleaf's github repository with a request to support adding of custom "boolean attributes" conditionally.

michal.jakubeczy Over a year ago

yeah, might be a good one. Is is still maintained btw?

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