handle errors with HTMX - htmx

Question

<form
class="" id="form" hx-post="/add/" hx-swap="afterbegin" hx-target="#big_list" hx-trigger="submit">
<input type="text" name="langue1" >
<input type="text" name="langue2">
<div id="errors"></div>
<button type="submit">GO</button>
</form>
<div id="big_list">
.....
</div>
I have a big list in #big_list, and I want my #form appends only one row when submitted.
How with htmx, can I handle errors and show message in #errors ?

Answer 1

I created this solution so you can use hx-target-error = to define which HTML will be displayed after a failed request
document.body.addEventListener('htmx:afterRequest', function (evt) {
const targetError = evt.target.attributes.getNamedItem('hx-target-error')
if (evt.detail.failed && targetError) {
document.getElementById(targetError.value).style.display = "inline";
}
});
document.body.addEventListener('htmx:beforeRequest', function (evt) {
const targetError = evt.target.attributes.getNamedItem('hx-target-error')
if (targetError) {
document.getElementById(targetError.value).style.display = "none";
}
});

Answer 2

If your code raises the errors (validation?), you can change target and swap behavior with response headers.
Response.Headers.Add("HX-Retarget", "#errors");
Response.Headers.Add("HX-Reswap", "innerHTML");
If you want to return a status other than 200, you have to tell htmx to accept it.
4xx would normally not do a swap in htmx. In case of validation errors you could use 422.
document.body.addEventListener('htmx:beforeOnLoad', function (evt) {
if (evt.detail.xhr.status === 422) {
evt.detail.shouldSwap = true;
evt.detail.isError = false;
}
});
It works in htmx 1.8.
If you want to remove the error message on then next sucessfull request, you could use hx-swap-oob. Out of band elements must be in the top level of the response.
So the response could look like this:
<div>
your new row data...
</div>
<div id="errors" hx-swap-oob="true"></div>
Update
You can now use the new powerful extension multi-swap to swap multiple elements arbitrarily placed and nested in the DOM tree.
See https://htmx.org/extensions/multi-swap/

Answer 3

Although it doesn't follow REST principles, you might consider using an swap-oob to report your error back to your user. For example, your request might return a (slightly misleading) status 200, but include content like this:
<div id="errors" hx-swap-oob="true">
There was an error processing your request...
</div>
If it's important to follow REST more precisely, then you'll want to listen to the htmx:responseError event, as mentioned by #guettli in his previous answer.