JSFiddle - React, Tailwind, and code Playground

HTML

<a id="anchor" download="sample.chr">sample.chr</a>

JavaScript

"use strict";

onload = function() {
	let data = new Uint8Array(8192);
	data.fill(0);

	let pat = [
		[0x00,0x00,0x00,0x30, 0x30,0x00,0x00,0x00],	// right
		[0x00,0x00,0x00,0xc0, 0xc0,0x00,0x00,0x00],	// left
		[0x00,0x00,0x00,0x00, 0x00,0x60,0x60,0x00],	// down
		[0x00,0x60,0x60,0x00, 0x00,0x00,0x00,0x00],	// up

		[0x00,0x0c,0x0c,0x00, 0x00,0x00,0x00,0x00],	// start
		[0x00,0x03,0x03,0x00, 0x00,0x00,0x00,0x00],	// select
		[0x00,0x00,0x00,0x00, 0x00,0x0c,0x0c,0x00],	// B
		[0x00,0x00,0x00,0x00, 0x00,0x03,0x03,0x00],	// A
	];
	for (let k = 0; k < 256; k++) {
		for (let j = 0; j < 8; j++) {
			if ((k>>j) & 1) {
				for (let i = 0; i < 8; i++) {
					data[k*16+i] |= pat[j][i];
				}
			}
		}
	}

	let p00 = [0x01,0x01,0x01,0x01, 0x01,0x01,0x01,0xff];
	for (let i = 0; i < 8; i++) {
		data[8+i] |= p00[i];
	}

	let blob = new Blob([data.buffer]);
	let url = URL.createObjectURL(blob);
	anchor.href = url;
};