First things first, make sure you've got Node.js and npm already set up on your machine. Then, to get the Supabase CLI, just run this command:

npm install -g supabase

Alright, now let's get Supabase going in your project directory. Head over to your project folder and type this in your terminal:

supabase init

This will create a supabase folder with all the services and a .env file for your environment variables. Pretty neat, right?

Next up, let's fire up the local Supabase development environment. Just run:

supabase start

Now your local Supabase should be up and running. You can interact with the database by going to http://localhost:8000. Here, you can create tables, insert data, and do all the usual CRUD stuff.

To connect Supabase with your JavaScript app, install the @supabase/supabase-js library:

npm install @supabase/supabase-js

Then, in your JavaScript file, set up the connection like this:

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

const supabaseUrl = 'http://localhost:8000' // Use your own url
const supabaseKey = 'examplekey' // Use your own key from .env file

const supabase = createClient(supabaseUrl, supabaseKey)

Now, let's fetch some data from your Supabase database:

let { data: posts, error } = await supabase
  .from('posts')
  .select('*')
  .order('id', { ascending: true })

To get D3.js, just run this command:

npm install d3

Now, you can use D3.js to create some cool visualizations. Import D3.js and use the data you fetched from Supabase to make charts, graphs, and more.

Here's a simple example to get you started:

import * as d3 from "d3";

var data = [80, 90, 100, 110];

var svg = d3.select("body")
  .append("svg")
  .attr("width", 500)
  .attr("height", 500);

svg.selectAll("rect")
  .data(data)
  .enter()
  .append("rect")
  .attr("x", function(d, i) {
    return i * 70;  
  })
  .attr("y", function(d) {
    return 500 - 3 * d; 
  })
  .attr("width", 65)
  .attr("height", function(d) {
    return 3 * d; 
  });

This is just a basic example, but you can use D3.js to create more complex and interactive visualizations with the data from your Supabase database. Have fun experimenting!