안전한 할당

const [error, value] ?= maybeThrows();

let errorMsg;

try {
  maybeThrow();
} catch (e) {
  errorMsg = "An error message";
}

function tryCatch(fn, ...args) {
  try {
    return [undefined, fn.apply(null, args)]
  } catch (e) {
    return [e, undefined];
  }
}

function throws() {
  throw new Error("It threw");
}

// returns a sum
// prints [ undefined, 2 ]
console.log(tryCatch(Math.sqrt, 4));

// returns an error
// prints [ Error: 'It threw', undefined ]
console.log(tryCatch(throws));

console.log(tryCatch(() => {
  throw new Error("It threw");
}));

function tryCatch(fn, ...args) {
  try {
    const result = fn.apply(null, args);

    if (result.then) {
      return new Promise(resolve => {
          result
            .then(v => resolve([undefined, v]))
            .catch(e => resolve([e, undefined]))  
      }); 
    }

    return [undefined, result];
  } catch (e) {
    return [e, undefined];
  }
}

function throws() {
  throw new Error("It threw");
}

async function asyncSum(first, second) {
  return first + second;
}

async function asyncThrows() {
  throw new Error("It throws async");
}

// returns a sum
// prints [ undefined, 2 ]
console.log(tryCatch(Math.sqrt, 4));

// returns an error
// prints [ Error: 'It threw', undefined ]
console.log(tryCatch(throws));

// returns a promise resolving to value
// prints [ undefined, 3 ]
console.log(await tryCatch(asyncSum, 1, 2));

// returns a promise resolving to error
// prints [ Error: 'It throws async', undefined ]
console.log(await tryCatch(asyncThrows));

if (result.then) {
  return new Promise(resolve => {
      result
        .then(v => resolve([undefined, v]))
        .catch(e => resolve([e, undefined]))    
  }); 
}