Eager vs. Lazy Comparison

timeline comparison

code change

// BEFORE Chrome 149 — identical code, but eager under the hood
const items = await navigator.clipboard.read();
// ^ All format data fetched here (slow for large clipboards)

for (const item of items) {
  const blob = await item.getType('text/plain');
  // ^ Just returns the already-loaded blob — fast, but wasted work above
}

// AFTER Chrome 149 — same code, lazy under the hood
const items = await navigator.clipboard.read();
// ^ Only type list fetched — fast even with large clipboard

for (const item of items) {
  // Only items that call getType() trigger an OS clipboard read:
  if (item.types.includes('text/plain')) {
    const blob = await item.getType('text/plain');
    // ^ Fetches only text/plain from the OS — skips image/png, text/html
  }
}

// No code change required — Chrome 149 makes this automatically lazy

what sites benefit most

• Rich text editors that only need text/html but the clipboard has a large image
• Search boxes that paste plain text and discard the HTML/image formats
• Format detectors that check item.types to choose a paste handler — now free to inspect without reading data
• Multi-clipboard-item UIs that list available items before the user selects one

see also

• Lazy Read Demo — step-through interactive demo
• ChromeStatus entry
• MDN — Clipboard.read()