Easy console.log() inside one liner functions

#javascript #webdev #codenewbie

Let's say we want to log obj inside this .map() function here:

const arr = [
  { val: 1 },
  { val: 2 },
  { val: 3 }
];

const nums = arr.map(obj => obj.val*2);

Well, dang! Now we have to convert this to a multi-line function, right?

const nums = arr.map(obj => {
  console.log(obj);
  return obj.val * 2;
});

Instead we can use the logical OR (||) operator with console.log() to short-circuit evaluate the return statement:

const nums = arr.map(obj => console.log(obj) || obj.val*2);

This works because console.log() evaluates to undefined so our OR (||) opertator will evalutate the next operand which is the return portion of the function and will return the same result as the original example!

This is especially usefull with JSX where we commonly render components with implicit return statements:

export default function App() {
  return (
    <div>
      <h2>Short-circuit Logging</h2>
      <ul>
        {nums.map((num) => console.log(num) || (
          <li key={num}>{num}</li>
        ))}
      </ul>
    </div>
  );
}

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Top comments (9)

Jon Randy 🎖️ • Nov 11 '21 • Edited

You could also wrap your function with a logger wrapper function. Ending up with something like:

nums.map(logged(num => <li key={num}>{num}</li>))

The function returned by your logged wrapper function would log inputs, outputs, whatever; as well as calling the passed function and returning its result. This way you could have consistent logging everywhere, and switch it off at a stroke just by modifying the logged function

JS Bits Bill • Nov 11 '21

I like this!

Jon Randy 🎖️ • Nov 11 '21

If you wanted them fully removed though, you would still need to do that. The wrapped versions of the functions will be slower than the originals

Furkan KAYA • Nov 11 '21 • Edited

I think your third example won't work because in the first mapping console.log will not return anything, so you will have an array of undefineds for second map function. I might be wrong but I think it's going to be like this.