typescritpt: get file input accept

getFileInputAccept.ts

import { filter, includes, map } from "lodash";

export const AcceptFileExtensions = <const>{
  JPG: "jpg",
  JPEG: "jpeg",
  PNG: "png",
  PDF: "pdf",
};

export type AcceptFileExtensions = typeof AcceptFileExtensions[keyof typeof AcceptFileExtensions];

/**
 * 拡張子群を元に、input type="file" のaccept部分を生成
 *
 * @export
 * @param {AcceptFileExtensions[]} fileExtensions
 * @returns
 */
export default function getFileInputAccept(fileExtensions: AcceptFileExtensions[]) {
  // type check してるのでいらないはずだけど一応 filter
  const filteredExtensions = filter(fileExtensions, (ext) =>
    includes(Object.values(AcceptFileExtensions), ext)
  );

  return map(filteredExtensions, (ext) => {
    switch (ext) {
      case AcceptFileExtensions.JPG:
      case AcceptFileExtensions.JPEG:
      case AcceptFileExtensions.PNG:
        return `image/${ext}`;
      case AcceptFileExtensions.PDF:
        return `application/${ext}`;
      // type check & filter してるのでdefaultは通らないはず
      default:
        console.error("[getFileAccept]: should set corrected file extension.");
        return "";
    }
  }).join(",");
}