Supabase Backend as a Service · Lesson

Storing Files in Supabase Buckets

Understand how to create and manage storage buckets, and programmatically upload various file types to your Supabase project.

Storing Files in Supabase Buckets is a free Supabase Backend as a Service lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Supabase Backend as a Service learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Welcome to Supabase Storage

Managing files like images, videos, and documents is crucial for many apps. Supabase offers a robust, S3-compatible object storage solution right out of the box!

It's designed for scalability and security, letting you store and serve user-generated content or application assets with ease.

Understanding Storage Buckets

Think of a bucket as a top-level folder or container for your files. Each Supabase project can have multiple buckets.

Organize files by type (e.g., avatars, product-images).
Set different security rules for each bucket.
Buckets are isolated, meaning files in one bucket don't mix with another.

Create a Bucket in the Dashboard

You can create buckets directly from the Supabase Dashboard. Navigate to the Storage section and click "New bucket".

Give it a unique name and decide if it should be public or private. We'll explore these options next!

Public or Private Access?

This is a key decision when creating a bucket:

Public Buckets: Anyone with the URL can access files. Great for static assets like profile pictures or public documents.
Private Buckets: Files require authentication and specific policies to be accessed. Ideal for sensitive user data or premium content.

You can change this setting later, but it's good to plan ahead!

Setting Up for Uploads (JS)

To upload files from your app, you'll use the Supabase client library. First, ensure you have your Supabase URL and anon key initialized.

We'll use a simple JavaScript example. Imagine supabase is your initialized client.

import { createClient } from '@supabase/supabase-js';

const SUPABASE_URL = 'YOUR_SUPABASE_URL';
const SUPABASE_ANON_KEY = 'YOUR_ANON_KEY';

const supabase = createClient(SUPABASE_URL, SUPABASE_ANON_KEY);

console.log('Supabase client initialized.');

Programmatically Upload a File

The storage.from().upload() method is your go-to for uploading. It needs the bucket name, the path within the bucket, and the file itself.

Let's simulate uploading a simple text file. In a real app, you'd get the file from an HTML <input type="file">.

import { createClient } from '@supabase/supabase-js';

const SUPABASE_URL = 'YOUR_SUPABASE_URL';
const SUPABASE_ANON_KEY = 'YOUR_ANON_KEY';

const supabase = createClient(SUPABASE_URL, SUPABASE_ANON_KEY);

async function uploadFile() {
  // In a real app, 'file' would come from an input element
  const mockFile = new File(['Hello CoddyKit!'], 'hello.txt', {
    type: 'text/plain',
  });

  const { data, error } = await supabase.storage
    .from('my-first-bucket') // Replace with your bucket name
    .upload('public/hello_world.txt', mockFile);

  if (error) {
    console.error('Upload error:', error.message);
  } else {
    console.log('Upload successful:', data);
  }
}

uploadFile();

File Paths & Overwrite Behavior

The 'path' in .upload('path/to/file.txt', file) determines where your file lands within the bucket.

'my-image.jpg': Uploads to the bucket's root.
'avatars/user123.png': Creates an avatars folder if it doesn't exist.

By default, uploading to an existing path will overwrite the old file. You can control this with the upsert option.

Controlling Overwrites with Upsert

The upsert option in the upload method lets you decide what happens if a file with the same path already exists.

upsert: true (default): Overwrites the existing file.
upsert: false: Returns an error if a file with the same path exists, preventing accidental overwrites.

Use upsert: false when you want to ensure unique file names.

import { createClient } from '@supabase/supabase-js';

const SUPABASE_URL = 'YOUR_SUPABASE_URL';
const SUPABASE_ANON_KEY = 'YOUR_ANON_KEY';

const supabase = createClient(SUPABASE_URL, SUPABASE_ANON_KEY);

async function uploadUniqueFile() {
  const mockFile = new File(['Unique content!'], 'unique.txt', {
    type: 'text/plain',
  });

  // This will fail if 'public/unique.txt' already exists
  const { data, error } = await supabase.storage
    .from('my-first-bucket') // Replace with your bucket name
    .upload('public/unique.txt', mockFile, { upsert: false });

  if (error) {
    console.error('Upload failed (file exists or other error):', error.message);
  } else {
    console.log('Unique upload successful:', data);
  }
}

uploadUniqueFile();

Handles All Your File Needs

Supabase Storage isn't limited to just images or text files. It can handle any file type you throw at it!

Images: PNG, JPG, GIF, SVG
Videos: MP4, MOV, WebM
Documents: PDF, DOCX, XLSX
Audio: MP3, WAV

Just ensure your client-side code provides the correct file object.

Quick Check on Buckets

You've learned about Supabase Storage buckets and how to upload files. Let's test your understanding!

Recap: Storing Files

Great job! You've learned the fundamentals of Supabase Storage:

What buckets are and how to create them.
The difference between public and private buckets.
How to programmatically upload files using the Supabase client.
Controlling file overwrites with the upsert option.

Next, you'll dive into securing your files with Storage Policies!

Frequently asked questions

Is the “Storing Files in Supabase Buckets” lesson free?

Yes — the full text of “Storing Files in Supabase Buckets” is free to read here on the web, and the Supabase Backend as a Service course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Supabase Backend as a Service course, upgrade to CoddyKit PRO.

What will I learn in “Storing Files in Supabase Buckets”?

Understand how to create and manage storage buckets, and programmatically upload various file types to your Supabase project. You practise Supabase Backend as a Service with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Supabase Backend as a Service?

No prior experience is required. Supabase Backend as a Service on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Storing Files in Supabase Buckets” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Supabase Backend as a Service lesson?

Yes. Every Supabase Backend as a Service lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

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