Build forms with API routes

An HTML form causes the browser to refresh the page or navigate to a new one. To send form data to an API endpoint instead, you must intercept the form submission using JavaScript.

This recipe shows you how to send form data to an API endpoint and handle that data.

Prerequisites

Section titled Prerequisites

• A project with SSR (output: 'server') enabled
• A UI Framework integration installed

Recipe

Section titled Recipe

1. Create a form component using your UI framework. Each input should have a name attribute that describes the value of that input.

   Be sure to include a <button> or <input type="submit"> element to submit the form.

   Preact

   src/components/FeedbackForm.tsx

   export default function Form() {
     return (
       <form>
         <label>
           Name
           <input type="text" id="name" name="name" required />
         </label>
         <label>
           Email
           <input type="email" id="email" name="email" required />
         </label>
         <label>
           Message
           <textarea id="message" name="message" required />
         </label>
         <button>Send</button>
       </form>
     );
   }

   React

   src/components/FeedbackForm.tsx

   export default function Form() {
     return (
       <form>
         <label>
           Name
           <input type="text" id="name" name="name" required />
         </label>
         <label>
           Email
           <input type="email" id="email" name="email" required />
         </label>
         <label>
           Message
           <textarea id="message" name="message" required />
         </label>
         <button>Send</button>
       </form>
     );
   }

   Solid

   src/components/FeedbackForm.tsx

   export default function Form() {
     return (
       <form>
         <label>
           Name
           <input type="text" id="name" name="name" required />
         </label>
         <label>
           Email
           <input type="email" id="email" name="email" required />
         </label>
         <label>
           Message
           <textarea id="message" name="message" required />
         </label>
         <button>Send</button>
       </form>
     );
   }

   Svelte

   src/components/FeedbackForm.svelte

   <form>
     <label>
       Name
       <input type="text" id="name" name="name" required />
     </label>
     <label>
       Email
       <input type="email" id="email" name="email" required />
     </label>
     <label>
       Message
       <textarea id="message" name="message" required />
     </label>
     <button>Send</button>
   </form>

   Vue

   src/components/FeedbackForm.vue

   <template>
     <form>
       <label>
         Name
         <input type="text" id="name" name="name" required />
       </label>
       <label>
         Email
         <input type="email" id="email" name="email" required />
       </label>
       <label>
         Message
         <textarea id="message" name="message" required />
       </label>
       <button>Send</button>
     </form>
   </template>

2. Create the POST API endpoint that will receive the form data. Use request.formData() to process it. Be sure to validate the form values before you use them.

   This example sends a JSON object with a message back to the client.

   src/pages/api/feedback.ts

   import type { APIRoute } from "astro";
   
   export const POST: APIRoute = async ({ request }) => {
     const data = await request.formData();
     const name = data.get("name");
     const email = data.get("email");
     const message = data.get("message");
     // Validate the data - you'll probably want to do more than this
     if (!name || !email || !message) {
       return new Response(
         JSON.stringify({
           message: "Missing required fields",
         }),
         { status: 400 }
       );
     }
     // Do something with the data, then return a success response
     return new Response(
       JSON.stringify({
         message: "Success!"
       }),
       { status: 200 }
     );
   };

3. Create a function that accepts a submit event, then pass it as a submit event handler to your form. In the function, call preventDefault on the event to override the browser’s default submission process.

   Then, create a FormData object and send it to your endpoint using fetch.

   Preact

   src/components/FeedbackForm.tsx

   import { useState } from "preact/hooks";
   
   export default function Form() {
     const [responseMessage, setResponseMessage] = useState("");
   
     async function submit(e: SubmitEvent) {
       e.preventDefault();
       const formData = new FormData(e.target as HTMLFormElement);
       const response = await fetch("/api/feedback", {
         method: "POST",
         body: formData,
       });
       const data = await response.json();
       if (data.message) {
         setResponseMessage(data.message);
       }
     }
   
     return (
       <form onSubmit={submit}>
         <label>
           Name
           <input type="text" id="name" name="name" required />
         </label>
         <label>
           Email
           <input type="email" id="email" name="email" required />
         </label>
         <label>
           Message
           <textarea id="message" name="message" required />
         </label>
         <button>Send</button>
         {responseMessage && <p>{responseMessage}</p>}
       </form>
     );
   }

   React

   src/components/FeedbackForm.tsx

   import { FormEvent, useState } from "react";
   
   export default function Form() {
     const [responseMessage, setResponseMessage] = useState("");
   
     async function submit(e: FormEvent<HTMLFormElement>) {
       e.preventDefault();
       const formData = new FormData(e.target as HTMLFormElement);
       const response = await fetch("/api/feedback", {
         method: "POST",
         body: formData,
       });
       const data = await response.json();
       if (data.message) {
         setResponseMessage(data.message);
       }
     }
   
     return (
       <form onSubmit={submit}>
         <label htmlFor="name">
           Name
           <input type="text" id="name" name="name" autoComplete="name" required />
         </label>
         <label htmlFor="email">
           Email
           <input type="email" id="email" name="email" autoComplete="email" required />
         </label>
         <label htmlFor="message">
           Message
           <textarea id="message" name="message" autoComplete="off" required />
         </label>
         <button>Send</button>
         {responseMessage && <p>{responseMessage}</p>}
       </form>
     );
   }

   Solid

   src/components/FeedbackForm.tsx

   import { createSignal, createResource, Suspense } from "solid-js";
   
   async function postFormData(formData: FormData) {
     const response = await fetch("/api/feedback", {
       method: "POST",
       body: formData,
     });
     const data = await response.json();
     return data;
   }
   
   export default function Form() {
     const [formData, setFormData] = createSignal<FormData>();
     const [response] = createResource(formData, postFormData);
   
     function submit(e: SubmitEvent) {
       e.preventDefault();
       setFormData(new FormData(e.target as HTMLFormElement));
     }
   
     return (
       <form onSubmit={submit}>
         <label>
           Name
           <input type="text" id="name" name="name" required />
         </label>
         <label>
           Email
           <input type="email" id="email" name="email" required />
         </label>
         <label>
           Message
           <textarea id="message" name="message" required />
         </label>
         <button>Send</button>
         <Suspense>{response() && <p>{response().message}</p>}</Suspense>
       </form>
     );
   }

   Svelte

   src/components/FeedbackForm.svelte

   <script lang="ts">
     let responseMessage: string;
   
     async function submit(e: SubmitEvent) {
       e.preventDefault();
       const formData = new FormData(e.currentTarget as HTMLFormElement);
       const response = await fetch("/api/feedback", {
         method: "POST",
         body: formData,
       });
       const data = await response.json();
       responseMessage = data.message;
     }
   </script>
   
   <form on:submit={submit}>
     <label>
       Name
       <input type="text" id="name" name="name" required />
     </label>
     <label>
       Email
       <input type="email" id="email" name="email" required />
     </label>
     <label>
       Message
       <textarea id="message" name="message" required />
     </label>
     <button>Send</button>
     {#if responseMessage}
       <p>{responseMessage}</p>
     {/if}
   </form>

   Vue

   src/components/FeedbackForm.vue

   <script setup lang="ts">
   import { ref } from "vue";
   
   const responseMessage = ref<string>();
   
   async function submit(e: Event) {
     e.preventDefault();
     const formData = new FormData(e.currentTarget as HTMLFormElement);
     const response = await fetch("/api/feedback", {
       method: "POST",
       body: formData,
     });
     const data = await response.json();
     responseMessage.value = data.message;
   }
   </script>
   <template>
     <form @submit="submit">
       <label>
         Name
         <input type="text" id="name" name="name" required />
       </label>
       <label>
         Email
         <input type="email" id="email" name="email" required />
       </label>
       <label>
         Message
         <textarea id="message" name="message" required />
       </label>
       <button>Send</button>
       <p v-if="responseMessage">{{ responseMessage }}</p>
     </form>
   </template>