support for try/catch expressions:

[graingert]

I expect this to work:

const foo = () => do { throw new Error('foo'); };
const bar = () => 3;
const res = do {
  try { foo(); } catch (e) { bar(); }
}
console.log(res); // 3;

But I get undefined;

babel transpiles to:

const foo = () => function () {
  throw new Error('foo');
}();
const bar = () => 3;
const res = function () {
  try {
    return foo();
  } catch (e) {
    bar();
  }
}();
console.log(res); // 3;

but I expected:

const foo = () => function () {
  throw new Error('foo');
}();
const bar = () => 3;
const res = function () {
  try {
    return foo();
  } catch (e) {
    return bar();
  }
}();
console.log(res); // 3;

an alternative that works is:

const foo = () => do { throw new Error('foo'); };
const bar = () => 3;
const res = do { try { foo(); } catch (e) {} } || bar();
console.log(res); // 3;

[graingert]

I'd also like to see an implicit catch { } on try expressions.

const foo = () => do { throw new Error('foo'); };
const bar = () => 3;
const res = do { try { foo(); } } || bar();
console.log(res); // 3;

[claudepache]

@graingert This is a bug in Babel, your expectation is correct.

As for the “implicit catch” wish, this is unrelated to this proposal. I’ll just mention that it has been recently discussed on es-discuss: https://esdiscuss.org/topic/an-operator-for-ignoring-any-exceptions

[Jessidhia]

What should happen if there is a finally block? If it is anything but an empty block, it potentially overrides the completion value of the try or catch block, unless any potential completion value of finally is always ignored.

[claudepache]

@Kovensky According to the spec, completion value of a finally block is ignored, unless it is an abrupt completion.