const fs = require('fs');
const { promisify } = require('util');
const decode = require('heic-decode');
(async () => {
  const buffer = await promisify(fs.readFile)('/path/to/my/image.heic');
  const {
    width,  // integer width of the image
    height, // integer height of the image
    data    // Uint8ClampedArray containing pixel data
  } = await decode({ buffer });
})();

const fs = require('fs');
const { promisify } = require('util');
const decode = require('heic-decode');
(async () => {
  const buffer = await promisify(fs.readFile)('/path/to/my/multi-image.heic');
  const images = await decode.all({ buffer });
  for (let image of images) {
    // decode and use each image individually
    // so you don't run out of memory
    const {
      width,  // integer width of the image
      height, // integer height of the image
      data    // Uint8ClampedArray containing pixel data
    } = await image.decode();
  }
  // when you are done, make sure to free all memory used to convert the images
  images.dispose();
})();