One-liner to set a variable value using a function and throw if it is falsy

Question

I find myself using the following pattern a lot when working with json data that may or may not be corrupt:

function getFooId(json) {
  const id = json.foo.id;
  if (!id) {
    throw Error(`foo.id has not been defined`);
  }
  return id;
}

This seems overly verbose. I would like a one-liner along the lines of:

function getBarId(json) {
  return json.bar.id? json.bar.id : throw Error(`bar.id has not been defined`);
}

Can this be done?

Answer 1

There's a proposal for throw expressions that would allow you to do this really concisely, but it's still at stage 2 - it hasn't been implemented yet.

Currently, throw must be a statement , like an if statement or a function declaration - it can't be in an expression context. To achieve this, you could alternate the id variable with an IIFE, where the first (and only) line of the IIFE throws;

function getBarId({ bar: { id }}) {
  return id || (() => { throw new Error(`bar.id has not been defined`); })();
}

But I still prefer your first method, it's more readable:

function getBarId({ bar: { id }}) {
  if (id) return id;
  throw new Error(`bar.id has not been defined`);
}

Answer 2

This also a better way to handle the error

  function getBarId({bar:{id}}) {
   return new Promise((resolve,reject)=>{ id ? resolve(id) : reject(`bar.id has not 
   been defined`)})
   }