@shipengine/connect-carrier-api/src/app/metadata/custom-validators/file-exists.ts

This is the typescript/javascript definitions for carrier api

import { existsSync } from 'fs';

export const fileExists = (value: string, helpers: any) => {
  if (existsSync(value)) {
    return value;
  }
  throw new Error("the file doesn't exist");
};