Part 3 / Forms / The <form> element

In the previous chapter, we saw how to get data from the server to the browser. Sometimes you need to send data in the opposite direction, and that's where <form> — the web platform's way of submitting data — comes in.

Let's build a todo app. We've already got an in-memory database set up in src/lib/server/database.js, and our load function in src/routes/+page.server.js uses the cookies API so that we can have a per-user todo list, but we need to add a <form> to create new todos:

<h1>Todos</h1>

<form method="POST">
	<label>
		add a todo:
		<input
			name="description"
			autocomplete="off"
		/>
	</label>
</form>

{#each data.todos as todo}

If we type something into the <input> and hit Enter, the browser makes a POST request (because of the method="POST" attribute) to the current page. But that results in an error, because we haven't created a server-side action to handle the POST request. Let's do that now:

import * as db from '$lib/server/database.js';

export function load({ cookies }) {
	// ...
}

export const actions = {
	default: async ({ cookies, request }) => {
		const data = await request.formData();
		db.createTodo(cookies.get('userid'), data.get('description'));
	}
};

When we hit Enter, the database is updated and the page reloads with the new data.

Notice that we haven't had to write any fetch code or anything like that — data updates automatically. And because we're using a <form> element, this app would work even if JavaScript was disabled or unavailable.