makePlaceholder.js

const cache = {};
export function makePlaceholder(width, height) {
  const key = `${width}x${height}`;
  if (!cache[key]) {
    cache[key] = 'data:image/svg+xml;base64,' + window.btoa(
      `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 ${width} ${height}">
      <rect width="${width}" height="${height}" fill="#f0f0f0"/>
    </svg>`
    );
  }
  return cache[key];
}