A simple HEIC to JPEG-implementation for Node using libheif-js (https://www.npmjs.com/package/libheif-js) and canvas (https://www.npmjs.com/package/canvas). Not type safe, should be refined. Based of catdad-experiments/heic-convert.

heic2jpeg.ts

import libheif from 'libheif-js';
import { ImageData, Canvas, createCanvas } from 'canvas'

type Props = {
  buffer: Buffer;
  quality: number;
};

const processSingleImage = (image: any): Promise<any> => {
	return new Promise((resolve, reject) => {
		const w = image.get_width();
		const h = image.get_height();
		const whiteImage: any = new ImageData(w, h);
		for (let i = 0; i < w * h; i++) {
			whiteImage.data[i * 4 + 3] = 255;
		}
		image.display(whiteImage, (imageData: any) => {
			if (!imageData) {
				return reject(
					"ERR_LIBHEIF Error while processing single image and generating image data, could not ensure image"
				);
			}
			resolve(imageData);
		});
	});
};

const decodeBuffer = (buffer: Buffer): Promise<any> => {
  return new Promise(async (resolve, reject) => {
  const decoder = new libheif.HeifDecoder();
    let imagesArr = decoder.decode(buffer);
    imagesArr = imagesArr.filter((x: any) => {
			let valid = true;
			try {
				/*
				sometimes the heic container is valid
				yet the images themselves are corrupt
				*/
				x.get_height();
			} catch (e) {
				valid = false;
			}
			return valid;
		});
		if (!imagesArr.length) {
			reject('No valid images found');
		}

    imagesArr = await Promise.all(imagesArr.map((image: libheif.DecodeResult) => processSingleImage(image)));
    resolve(imagesArr);
  });
}

const imageDataToBlob = ({
  imageData,
  quality = 0.92,
}: {
  imageData: any;
  toType?: string;
  quality?: number;
}): Promise<Blob> => {
  // normalize quality
  if (quality > 1 || quality < 0) {
    quality = 0.92;
  }
  return new Promise((resolve, reject) => {
    let canvas: Canvas | null = null;

    try {
      canvas = createCanvas(imageData.width, imageData.height);
    } catch (e) {}

    if (!canvas) {
      return reject(
        "ERR_CANVAS Error on converting imagedata to blob: Could not create canvas element"
      );
    }

    const ctx = canvas.getContext("2d");
    if (!ctx) {
      return reject(
        "ERR_CANVAS Error on converting imagedata to blob: Could not get canvas context"
      );
    }
    ctx.putImageData(imageData as ImageData, 0, 0);

    // Convert canvas to buffer, then to blob, then resolve
    const buf = canvas.toBuffer('image/jpeg', { quality: quality });
    resolve(new Blob([buf], { type: 'image/jpeg' }));
  });
};

export const heic2jpeg = ({ buffer, quality }: Props): Promise<Blob[]> => {
  return new Promise(async (resolve, reject) => {
    const imagesArr = await decodeBuffer(buffer);
    const files = await Promise.all(
      imagesArr.map((imageData: any) =>
        imageDataToBlob({
          imageData,
          quality,
        })
      )
    );
    resolve(files);  
  });
};