Ajax Form Response Status Codes

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Open the modal and fill out the name and price fields: the only two required fields. I want to see what happens if we submit the form successfully.

And... whoa! That was weird. On success, our controller currently redirects back to /admin/product. When jQuery's Ajax hits a redirect, it follows it and makes a second Ajax request. We can see this in the Network tab: here's the original request and here's the request from the redirect. And because that redirects to the list page, it grabbed the full HTML for that page and jammed it into the modal.

That's... probably not what we want. Instead, I want to close the modal. But to do that, we need to be able to determine - from JavaScript - whether a form submit was successful or had a validation error.

But, at the very least, if we refresh the page, we do see the new product in the list. So, yay! We know the save part is working.

On Success: 204 Empty Response

Over in the controller, if the form is submitted via Ajax, instead of a redirect, what should we return? How about an empty, successful response. We can do that with if $request->isXmlHttpRequest() - or you might instead be looking for a query parameter if you decided to use that strategy - then return new Response() - the one from HttpFoundation - passing it null for the content and 204 for the status code.

... lines 1 - 15
class ProductAdminController extends AbstractController
{
... lines 18 - 30
public function new(Request $request): Response
{
... lines 33 - 36
if ($form->isSubmitted() && $form->isValid()) {
... lines 38 - 41
if ($request->isXmlHttpRequest()) {
return new Response(null, 204);
}
return $this->redirectToRoute('product_admin_index');
}
... lines 48 - 57
}
... lines 59 - 102
}

204 is a special status code that means:

This response was successful! Yay! But... I have no content that I want to return.

So: an empty - but successful - response. That'll fix the redirect issue.

On Error: 422 Error Response

But there's still one problem. When the form has validation errors, we're currently returning a 200 success status code: that's what $this->render() uses by default.

In other words, whether the form submit is successful or not, both situations return a successful status code. That... doesn't make our life very easy in JavaScript where we need to figure out which situation we're in! Sure, we could look exactly for a 200 versus 204 status code... but... there's a better way.

What is it? Return an error status code when the form fails validation. This will not only make our life easier in JavaScript... it's also more correct! And it will still work fine if you're submitting a form normally without JavaScript: the error status code won't confuse old browsers or anything like that.

The third argument to render() is a Response object that the HTML from the template will be put into. When this is not passed, a Response object with a 200 status code is automatically created. Let's pass our own: new Response() - the same one from HttpFoundation - passing null for the for the content... because that's going to be replaced by the HTML from the template anyways.

The really important thing is the status code. But this render() method is called both when the form is originally loaded and when it's submitted with invalid data. So we need to figure out which situation we're in. Use the ternary syntax here to say: if $form->isSubmitted(), then use 422 else 200.

... lines 1 - 15
class ProductAdminController extends AbstractController
{
... lines 18 - 30
public function new(Request $request): Response
{
... lines 33 - 36
if ($form->isSubmitted() && $form->isValid()) {
... lines 38 - 41
if ($request->isXmlHttpRequest()) {
return new Response(null, 204);
}
return $this->redirectToRoute('product_admin_index');
}
... lines 48 - 50
return $this->render('product_admin/' . $template, [
... lines 52 - 53
], new Response(
null,
$form->isSubmitted() && !$form->isValid() ? 422 : 200,
));
}
... lines 59 - 102
}

This works because - if the form was submitted and was successful - we would already be inside the first if statement... and we would never get down here. So if the form is submitted, we definitely know it's an invalid submit.

The 422 status code means "unprocessable entity". And it's a pretty standard status code for validation errors. As a bonus, doing this on your forms will play super nicely with Stimulus's sister technology Turbo. Oh, and by the way, in Symfony 5.3, there is a new renderForm() shortcut in your controller, which will automatically set the 422 status code for you on error. That'll make this much cleaner.

Try/Catch the Ajax Call

Back in our Stimulus controller, now we have the info we need. When the form submit fails validation, the 422 status code will cause the await $.ajax() to throw an exception. So let's wrap this in a try catch block.

Say, try, catch:

... lines 1 - 4
export default class extends Controller {
... lines 6 - 18
async submitForm(event) {
... lines 20 - 22
try {
await $.ajax({
url: this.formUrlValue,
method: $form.prop('method'),
data: $form.serialize(),
});
... line 29
} catch (e) {
... line 31
}
}
}

and what we want to do is take out this.modalBodyTarget.innerHTML because we only want to do that on error. In the catch, say this.modalBodyTarget.innerHTML and the response text is available on the error object as e.responseText.

... lines 1 - 4
export default class extends Controller {
... lines 6 - 18
async submitForm(event) {
... lines 20 - 22
try {
await $.ajax({
url: this.formUrlValue,
method: $form.prop('method'),
data: $form.serialize(),
});
... line 29
} catch (e) {
this.modalBodyTarget.innerHTML = e.responseText;
}
}
}

In the successful situation, for now, just console.log('success').

... lines 1 - 4
export default class extends Controller {
... lines 6 - 18
async submitForm(event) {
... lines 20 - 22
try {
await $.ajax({
url: this.formUrlValue,
method: $form.prop('method'),
data: $form.serialize(),
});
console.log('success!');
} catch (e) {
this.modalBodyTarget.innerHTML = e.responseText;
}
}
}

Ok team - let's see what happens! Refresh. Open the modal and let's first submit the form empty. Beautiful! We have errors! Fill in name and price... and submit again. Okay.... nothing happened. But if we check the console... yes! There's our log! All we need to do now is close the modal on success.

Closing the Modal on Success

We can do that by calling hide() on this modal object. The only problem is that... we don't have access to that object from down here in submitForm()! That's ok: this is where having a controller object comes in handy! We can set that modal on a property.

Up at the top of the class... we don't have to do this because JavaScript is friendly, but I'm going to say modal equals null to initialize the property. Then down in connect(), update to this.modal equals new Modal() and this.modal.show().

... lines 1 - 4
export default class extends Controller {
... lines 6 - 9
modal = null;
async openModal(event) {
... line 13
this.modal = new Modal(this.modalTarget);
this.modal.show();
... lines 16 - 17
}
... lines 19 - 34
}

Now, after the Ajax call, replace console.log('success') with this.modal.hide().

... lines 1 - 4
export default class extends Controller {
... lines 6 - 19
async submitForm(event) {
... lines 21 - 23
try {
... lines 25 - 29
this.modal.hide();
} catch (e) {
this.modalBodyTarget.innerHTML = e.responseText;
}
}
}

Let's try it now. Refresh - there's my awesome zip drive from the last submit - open the modal, fill out the field and... submit! OMG! We have a fully-functioning Ajax modal system. And... it's completely reusable!

The only imperfect thing is that we don't see the new item on the page, until we refresh. No worries: we'll handle that in the next chapter.

Listening to Bootstrap Modal Events

But before we do, search for "bootstrap 5 modal", click into its docs, and then go down to the "Events" section at the bottom. As the modal opens and closes, the modal itself dispatches some events. What if we needed to listen to those? Like, what if we need to run some custom code whenever a modal is closed. How can we do that? This is the beauty of Stimulus. We already know how! If something dispatches an event, all we need to do is add an action for that event.

Check it out: over in index.html.twig, I'll break this onto multiple lines and then add a data-action="". What we're going to do is listen to this hidden.bs.modal event, which happens after the modal is finished being hidden.

Use that event name, then ->, the name of our controller - modal-form - a # sign and then call the new method modalHidden.

... lines 1 - 5
<div class="container-fluid mt-4">
<div class="d-flex flex-row">
... lines 8 - 9
<div
... lines 11 - 13
data-action="hidden.bs.modal->modal-form#modalHidden"
>
... lines 16 - 23
</div>
</div>
... lines 26 - 65
</div>
... lines 67 - 68

Now, the hidden.bs.modal event won't be dispatched directly on this <div>. It will be dispatched on the modal element. But we already know that's okay! The event will bubble up to this <div>.

Copy modalHidden and head into our Stimulus controller. At the bottom add that method and let's just console.log('it was hidden').

... lines 1 - 4
export default class extends Controller {
... lines 6 - 35
modalHidden() {
console.log('it was hidden!');
}
}

Try it out! Go back to our site, refresh, open the modal and hit cancel. There's the log! Open it again, hit "X" and... another log. I love that.

Next: to make this a truly smooth user experience, after a successful form submit, what we should really do is make another Ajax call to reload the product list... so that the user can see the new product. Let's do that by, once again, making a reusable Stimulus controller. This controller will be able to reload the HTML for any element.

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What PHP libraries does this tutorial use?

// composer.json
{
    "require": {
        "php": ">=7.4.0",
        "ext-ctype": "*",
        "ext-iconv": "*",
        "composer/package-versions-deprecated": "1.11.99.1", // 1.11.99.1
        "doctrine/annotations": "^1.0", // 1.11.1
        "doctrine/doctrine-bundle": "^2.2", // 2.2.3
        "doctrine/doctrine-migrations-bundle": "^3.0", // 3.0.2
        "doctrine/orm": "^2.8", // 2.8.1
        "phpdocumentor/reflection-docblock": "^5.2", // 5.2.2
        "sensio/framework-extra-bundle": "^5.6", // v5.6.1
        "symfony/asset": "5.2.*", // v5.2.3
        "symfony/console": "5.2.*", // v5.2.3
        "symfony/dotenv": "5.2.*", // v5.2.3
        "symfony/flex": "^1.3.1", // v1.12.1
        "symfony/form": "5.2.*", // v5.2.3
        "symfony/framework-bundle": "5.2.*", // v5.2.3
        "symfony/property-access": "5.2.*", // v5.2.3
        "symfony/property-info": "5.2.*", // v5.2.3
        "symfony/proxy-manager-bridge": "5.2.*", // v5.2.3
        "symfony/security-bundle": "5.2.*", // v5.2.3
        "symfony/serializer": "5.2.*", // v5.2.3
        "symfony/twig-bundle": "5.2.*", // v5.2.3
        "symfony/ux-chartjs": "^1.1", // v1.2.0
        "symfony/validator": "5.2.*", // v5.2.3
        "symfony/webpack-encore-bundle": "^1.9", // v1.11.1
        "symfony/yaml": "5.2.*", // v5.2.3
        "twig/extra-bundle": "^2.12|^3.0", // v3.2.1
        "twig/intl-extra": "^3.2", // v3.2.1
        "twig/twig": "^2.12|^3.0" // v3.2.1
    },
    "require-dev": {
        "doctrine/doctrine-fixtures-bundle": "^3.4", // 3.4.0
        "symfony/debug-bundle": "^5.2", // v5.2.3
        "symfony/maker-bundle": "^1.27", // v1.30.0
        "symfony/monolog-bundle": "^3.0", // v3.6.0
        "symfony/stopwatch": "^5.2", // v5.2.3
        "symfony/var-dumper": "^5.2", // v5.2.3
        "symfony/web-profiler-bundle": "^5.2" // v5.2.3
    }
}

What JavaScript libraries does this tutorial use?

// package.json
{
    "devDependencies": {
        "@babel/preset-react": "^7.0.0", // 7.12.13
        "@popperjs/core": "^2.9.1", // 2.9.1
        "@symfony/stimulus-bridge": "^2.0.0", // 2.1.0
        "@symfony/ux-chartjs": "file:vendor/symfony/ux-chartjs/Resources/assets", // 1.1.0
        "@symfony/webpack-encore": "^1.0.0", // 1.0.4
        "bootstrap": "^5.0.0-beta2", // 5.0.0-beta2
        "core-js": "^3.0.0", // 3.8.3
        "jquery": "^3.6.0", // 3.6.0
        "react": "^17.0.1", // 17.0.1
        "react-dom": "^17.0.1", // 17.0.1
        "regenerator-runtime": "^0.13.2", // 0.13.7
        "stimulus": "^2.0.0", // 2.0.0
        "stimulus-autocomplete": "^2.0.1-phylor-6095f2a9", // 2.0.1-phylor-6095f2a9
        "stimulus-use": "^0.24.0-1", // 0.24.0-1
        "sweetalert2": "^10.13.0", // 10.14.0
        "webpack-bundle-analyzer": "^4.4.0", // 4.4.0
        "webpack-notifier": "^1.6.0" // 1.13.0
    }
}