Type Safe env.ts

createEnv.ts

export type BaseEnvRecord = Record<
  string,
  {
    value: string | undefined;
    required: boolean;
    defaultValue?: string;
  }
>;
export type ReturnTypeOfCreateEnv<T extends BaseEnvRecord> = {
  // If the value is required, it should be a string, otherwise it should be a string or undefined
  [K in keyof T]: T[K]["required"] extends true ? string : string | undefined;
};
export const createEnv = <T extends BaseEnvRecord>(
  envs: T,
): ReturnTypeOfCreateEnv<T> => {
  const result = new Map<string, string | undefined>();
  Object.entries(envs).forEach(([key, { value, required, defaultValue }]) => {
    if (required && !value && !defaultValue) {
      throw new Error(
        `Missing required environment variable: ${key}, value: ${value === undefined ? "undefined" : `"${value}"`}`,
      );
    }
    result.set(key, value || defaultValue);
  });
  return Object.fromEntries(result) as ReturnTypeOfCreateEnv<T>;
};

env.ts

import { createEnv } from "./createEnv.ts":
export const env = createEnv({
  /**
   * Next.jsサーバ自体のローカルホストURL
   */
  NEXT_PUBLIC_LOCALHOST_URL: {
    value: process.env["NEXT_PUBLIC_LOCALHOST_URL"],
    required: true,
    defaultValue: "http://localhost:3000",
  },
  /**
   * GraphQL APIのエンドポイントのURL
   */
  NEXT_PUBLIC_GRAPHQL_API_ENDPOINT: {
    value: process.env["NEXT_PUBLIC_GRAPHQL_API_ENDPOINT"],
    required: true,
    defaultValue: "http://localhost:4000/query",
  },
  /**
   * ローカルの開発モードかどうか
   */
  IS_DEVELOPMENT: {
    value: process.env["IS_DEVELOPMENT"],
    required: false,
    defaultValue: "false",
  }
});