getImageFileDimensions.tsx

/**
 * Get the dimensions of an image file
 * Check the mime type before calling this function
 */
export default function getImageFileDimensions(
  imageFile: File,
): Promise<{ width: number; height: number }> {
  return new Promise((resolve, reject) => {
    if (!(window.File && window.FileReader && window.FileList && window.Blob)) {
      reject(
        new Error('The File APIs are not fully supported in this browser.'),
      );
      return;
    }

    const reader = new FileReader();
    reader.onload = function () {
      const img = new Image();
      img.onload = function () {
        // image is loaded; sizes are available
        const { width, height } = img;
        resolve({ width, height });
      };
      img.onerror = function () {
        reject(new Error('There was an error loading the image'));
      };
      if (!reader.result) {
        reject(new Error('No reader result'));
        return;
      }
      img.src = reader.result.toString();
    };
    reader.readAsDataURL(imageFile);
  });
}