Create BMP (windows bitmap) file with JavaScript using ArrayBuffer

bmp.js

"use strict";

const fs    = require('fs')
    , path  = require('path')
;

const width     = 1000
    , height    = 1000
    , bpp       = 24    // Bits per pixel
;

process.on('unhandledRejection', error => {
    console.error('unhandledRejection', error.message);
});

(async function () {
    
    // https://en.wikipedia.org/wiki/BMP_file_format
    // Each row in the Pixel array is padded to a multiple of 4 bytes in size
    let rowSize         = Math.floor( (bpp * width + 31) / 32 ) * 4;
    let pixelArraySize  = rowSize * height;
    
    let BMP = new DataView(new ArrayBuffer(54));
    
    // Bitmap file header
    'BM'.split('').map( (v, i) => {
        BMP.setUint8(i, v.charCodeAt(0));
    });
    BMP.setUint32(2,  pixelArraySize + 54, true);   // File size (bytes): pixel array size + headers (=54 bytes)
    BMP.setUint16(6,  0, true);                     // Reserved
    BMP.setUint16(8,  0, true);                     // Reserved
    BMP.setUint32(10, 54, true);                    // Pixel array offset (=54 bytes)

    // DIB header, Windows BITMAPINFOHEADER
    BMP.setUint32(14, 40, true);                    // DIB header size (=40 bytes)
    BMP.setUint32(18, width, true);                 // Width in pixels
    BMP.setUint32(22, height, true);                // Height in pixels
    BMP.setUint16(26, 1, true);                     // Number of color planes (1)
    BMP.setUint16(28, bpp, true);                   // Bits per pixel
    BMP.setUint32(30, 0, true);                     // No compression (0)
    BMP.setUint32(34, pixelArraySize, true);        // Size of the raw bitmap data (bytes) including rows padding
    BMP.setUint32(38, 2835, true);                  // Horizontal resolution (pixels per metre, signed integer), 2835 dpm = 72 dpi
    BMP.setUint32(42, 2835, true);                  // Vertical resolution, 2835 dpm = 72 dpi
    BMP.setUint32(46, 0, true);                     // Number of colors in the palette (keep 0 for default 2^bpp)
    BMP.setUint32(50, 0, true);                     // Important colors (0 = every color is important)

    let bmpData = new DataView(new ArrayBuffer(pixelArraySize));

    // Offset of a pixel value
    let i = 0;
    let byesPerPixel = (bpp / 8) | 0;
    
    // From bottom row to the top
    for (let y = height - 1; y >= 0; y--) {
        for (let x = 0; x < width; x++) {

            bmpData.setUint8(i,       0); // B
            bmpData.setUint8(i + 1,   0); // G
            bmpData.setUint8(i + 2, 255); // R

            i += byesPerPixel;
        }
        i = rowSize * (height - y);
    }

    let buffer = Buffer.concat([
        Buffer.from(BMP.buffer),
        Buffer.from(bmpData.buffer)
    ]);
    
    let outFile = __dirname + '/out.bmp';
    fs.writeFileSync(outFile, buffer);

})();