runtime-env-cra/lib/generateConfig.js

A runtime environment handler for create-react-apps

const { constants } = require('fs');

const { generateJSON, constants: recConstants } = require('./utils');
const { promises: fsp } = require('fs');

const runtimeConfig = {};

async function generateConfig({ envConfig, envFile }) {
  let envConfigExists = true;

  try {
    await fsp.access(envConfig, constants.F_OK);
  } catch (err) {
    console.log(`${envConfig} does not exist. Creating one...`);
    envConfigExists = false;
  }

  if (envConfigExists) {
    await fsp.unlink(envConfig);
  }

  try {
    await fsp.access(envFile, constants.F_OK);
  } catch (err) {
    throw err;
  }

  const content = await fsp.readFile(envFile, 'utf8');

  content.split(/\r?\n/)
    .map((line) => line.split('#')[0].trim())
    .forEach((line) => {
      const equalSignIndex = line.indexOf('=');
      const lengthOfString = line.length;

      if (equalSignIndex !== -1) {
        const key = line.slice(0, equalSignIndex);
        const value = line.slice(equalSignIndex + 1, lengthOfString);

        if (process.env.NODE_ENV === recConstants.DEVELOPMENT) {
          runtimeConfig[key] = value;
        } else {
          if (!process.env[key])
            throw new Error(`Error getting '${key}' from process.env`);
          runtimeConfig[key] = process.env[key];
        }
      }
    });

  if (!Object.keys(runtimeConfig).length) {
    throw new Error(
      'Could not generate runtime config. Check your .env format!',
    );
  }

  const result = generateJSON(runtimeConfig);

  await fsp.writeFile(envConfig, result, 'utf-8');

  return result;
}

module.exports = generateConfig;