throwif operator

[Ron Buckton]

I’d much rather see something more like C# 7’s throw expressions: https://docs.microsoft.com/en-us/dotnet/articles/csharp/whats-new/csharp-7#throw-expressions

```js
// original example
fs.writeFile("message.txt", "Hello Node.js", err => err ? throw err : console.log("The file has been saved.");

// better example
function choose(kind) {
  return kind === 0 ? choseZero() : kind === 1 ? chooseOne() : throw new Error("out of range");
}
```

Ron

From: es-discuss [mailto:es-discuss-bounces at mozilla.org] On Behalf Of T.J. Crowder
Sent: Tuesday, April 11, 2017 5:20 AM
To: Elie Rotenberg <elie at rotenberg.io>
Cc: Нурбек <nurbek.ab at gmail.com>; es-discuss <es-discuss at mozilla.org>
Subject: Re: throwif operator

I don't think we need a new keyword for this, both because of Elie's point about handling it with a `throwif` function, and because Node's callback pattern is a bit old-fashioned in the world of promises and async/await. Until the Node API is updated to support promises natively, you can use one of the various "promisifying" libs to promisify the API:

```js
const pfs = /*...promisified version of fs*/;
```

...and then:

```js
pfs.writeFile("message.txt", "Hello Node.js")
    .then(() => console.log("The file has been saved."));
```

...and like your original code snippet, it will (on recent versions) terminate Node if you don't handle the error.

Combined with `async`/`await`, it becomes even cleaner:

```js
await pfs.writeFile("message.txt", "Hello Node.js");
console.log("The file has been saved.");
```

(Of course, that has to be within an `async` function.)

-- T.J. Crowder

On Tue, Apr 11, 2017 at 1:15 PM, Elie Rotenberg <elie at rotenberg.io<mailto:elie at rotenberg.io>> wrote:
const throwIf = (fn) => (err, ...args) => {
  if(err) throw err;
  return fn(...args);
};

...

fs.writeFile('message.txt', 'Hello Node.js', throwIf(() => console.log('The file has been saved')));


No need to extend the language and preempt keywords with stuff you can very easily implement in userland.
I'm not even convinced such a construct would be a good idea anyway to encourage rethrowing errors without thinking if it can be handled locally.

On Tue, Apr 11, 2017 at 2:06 PM, Нурбек <nurbek.ab at gmail.com<mailto:nurbek.ab at gmail.com>> wrote:
An example from node.js documentation:

fs.writeFile('message.txt', 'Hello Node.js', (err) => {
  if (err) throw err;
  console.log('The file has been saved!');
});

This looks like a common way to handle errors when the first parameter is an instance of Error.

Yes, this line of code is short and easy to copy-paste.
But introducing something like this:

fs.writeFile('message.txt', 'Hello Node.js', (err) => {
  throwif err;
  console.log('The file has been saved!');
});

would make the code much cleaner and bring some sort of standart way to handle such errors.

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