sample.ts

const { ENV_VAR_1, ENV_VAR_2, ENV_VAR_3 } = process.env;

const filterUndefinedVars = (vars: {
  [variableName: string]: any;
}): string[] => {
  return Object.entries(vars)
    .filter(([_k, v]) => typeof v === 'undefined')
    .map(([variableName]) => variableName);
};


const undefinedVars = filterUndefinedVars({
  ENV_VAR_1,
  ENV_VAR_2,
  ENV_VAR_3
});

if (undefinedVars.length >= 1) {
  undefinedVars.forEach((varName) => {
    console.error(`An environment variable ${varName} is not set.`);
  });
  throw new Error('One or more required environment variables are missing.');
}