Rotate image preview to compensate for EXIF orientation (Javascript / Typescript)

image-orientation.ts

// Based on: https://stackoverflow.com/a/46814952/283851

/**
 * Create a Base64 Image URL, with rotation applied to compensate for EXIF orientation, if needed.
 *
 * Optionally resize to a smaller maximum width - to improve performance for larger image thumbnails.
 */
export async function getImageUrl(file: File, maxWidth?: number) {
  return readOrientation(file)
    .then(orientation => applyRotation(file, orientation || 1, maxWidth || 999999));
}

/**
* @returns EXIF orientation value (or undefined)
*/
const readOrientation = (file: File) => new Promise<number|undefined>(resolve => {
  const reader = new FileReader();

  reader.onload = () => resolve((() => {
    const view = new DataView(reader.result as ArrayBuffer);

    if (view.getUint16(0, false) != 0xFFD8) {
      return;
    }

    const length = view.byteLength;

    let offset = 2;

    while (offset < length) {
      const marker = view.getUint16(offset, false);

      offset += 2;

      if (marker == 0xFFE1) {
        offset += 2;

        if (view.getUint32(offset, false) != 0x45786966) {
          return;
        }

        offset += 6;

        const little = view.getUint16(offset, false) == 0x4949;

        offset += view.getUint32(offset + 4, little);

        const tags = view.getUint16(offset, little);

        offset += 2;

        for (var i = 0; i < tags; i++) {
          if (view.getUint16(offset + (i * 12), little) == 0x0112) {
            return view.getUint16(offset + (i * 12) + 8, little);
          }
        }
      } else if ((marker & 0xFF00) != 0xFF00) {
        break;
      } else {
        offset += view.getUint16(offset, false);
      }
    }
  })());

  reader.readAsArrayBuffer(file.slice(0, 64 * 1024));
});

/**
* @returns Base64 Image URL (with rotation applied to compensate for orientation, if any)
*/
const applyRotation = (file: File, orientation: number, maxWidth: number) => new Promise<string>(resolve => {
  const reader = new FileReader();

  reader.onload = () => {
    const url = reader.result as string;

    const image = new Image();

    image.onload = () => {
      const canvas = document.createElement("canvas");
      const context = canvas.getContext("2d");

      let { width, height } = image;

      const [outputWidth, outputHeight] = orientation >= 5 && orientation <= 8
        ? [height, width]
        : [width, height];

      const scale = outputWidth > maxWidth ? maxWidth / outputWidth : 1;

      width = width * scale;
      height = height * scale;

      // set proper canvas dimensions before transform & export
      canvas.width = outputWidth * scale;
      canvas.height = outputHeight * scale;

      // transform context before drawing image
      switch (orientation) {
        // case 1: context.transform(1, 0, 0, 1, 0, 0); break;
        case 2: context.transform(-1, 0, 0, 1, width, 0); break;
        case 3: context.transform(-1, 0, 0, -1, width, height); break;
        case 4: context.transform(1, 0, 0, -1, 0, height); break;
        case 5: context.transform(0, 1, 1, 0, 0, 0); break;
        case 6: context.transform(0, 1, -1, 0, height, 0); break;
        case 7: context.transform(0, -1, -1, 0, height, width); break;
        case 8: context.transform(0, -1, 1, 0, 0, width); break;
        default: break;
      }

      // draw image
      context.drawImage(image, 0, 0, width, height);

      // export base64
      resolve(canvas.toDataURL("image/jpeg"));
    };

    image.src = url;
  }

  reader.readAsDataURL(file);
});