Compress images.
In the browser. Privately.

// compressImage() — the core logic
const options = {

  // File-size ceiling — set to original size so the library
  // never force-crushes beyond what initialQuality produces.
  maxSizeMB: imageData.original.size / (1024 * 1024),

  // ← THE real quality knob for JPEG / WebP / AVIF (0–1).
  // This is what the slider controls. Common mistake: using
  // maxSizeMB as a quality proxy — that only caps file size.
  initialQuality: quality / 100,

  // Prevent silent downscaling unless user sets px dimensions.
  alwaysKeepResolution: !hasResize,

  useWebWorker: true,   // non-blocking — UI stays responsive
  fileType: `image/${outputFormat}`,

  ...(hasResize && {
    maxWidthOrHeight: Math.max(Number(width) || 0, Number(height) || 0)
  }),
}

// Single file download — object URL + anchor click
const url = URL.createObjectURL(imageData.compressed)
const a   = document.createElement('a')
a.href     = url
a.download = `${name}_compressed.${outputFormat}`
document.body.appendChild(a); a.click()
URL.revokeObjectURL(url) // clean up — prevents memory leak

// Batch ZIP — JSZip bundles all compressed blobs
const zip  = new JSZip()
images.forEach(img => zip.file(`${name}.${fmt}`, img.compressed))
const blob = await zip.generateAsync({ type: 'blob' })