How can I access properties from older then calls?

Question

I used to code like this, and eventually found myself in a callback hell.

 Redis.get("boo", (res1) => {
      Redis.get(res1, (res2) => {
          console.log(res1);
          console.log(res2);
      });
 });

Howeever, when I do it like this:

Redis.getAsync("boo)
.then(res1 => {
    return Redis.getAsync(res1);
})
.then(res2 => {
    console.log(res1) // undefined
});

I cannot access res1 any longer. Passing parameters on each return feels dirty.

Any elegant solutions to this issue?

Another (dirty) solution would be to declare `res1` in the scope of the whole function. Based on how closure work, I doubt there is a cleaner way to do this. — DrakaSAN, Aug 31 '16 at 10:23

score 1 · Answer 1 · answered Aug 31 '16 at 10:22

1

Redis.getAsync("boo")
.then(res1 => {
    return Redis.getAsync(res1).then(res2 => ({res1, res2}));
})
.then(({res1, res2}) => {
    console.log(res1, res2);
});

answered Aug 31 '16 at 10:22

Maxx

1,740
10
17

This will lead back to callback hell, and OP chosed Promise to prevent exactly that. – DrakaSAN Aug 31 '16 at 10:24
how is this callback hell? I almost posted exactly the same answer :p so I'm biased – Jaromanda X Aug 31 '16 at 10:27
calback hell is when you go with callbacks deeper and deeper. You can't refuse callbacks at all, but you can create more clear code. – Maxx Aug 31 '16 at 10:29
is that shorthand syntax supported in nodejs yet? last time I checked (a long time ago) I don't think it worked – Jaromanda X Aug 31 '16 at 10:30
1

@JaromandaX Yes, it has been for a while (assuming you mean the arrow function). Destructuring not so much. – Ben Fortune Aug 31 '16 at 10:32
2

@DrakaSAN This isn't close to callback hell, since you're just passing the scope of `res1` into the next chain. – Ben Fortune Aug 31 '16 at 10:34
1

@DrakaSAN: no, there is no callback hell here, because you have at most two nested functions. – Bergi Aug 31 '16 at 10:47
(of course, [I'm slightly biased as well](http://stackoverflow.com/a/28250693/1048572)) – Bergi Aug 31 '16 at 10:48
I meant the shorthand object assignment – Jaromanda X Aug 31 '16 at 11:40
@Bergi @BenFortune: Right, I misread the code and thought he was chaining the `then` inside one another. Sorry about that. – DrakaSAN Aug 31 '16 at 12:30

score 0 · Answer 2 · answered Aug 31 '16 at 10:38

0

This is not officially supported but...

What about using aync/await if you are feeling adventurous and happy to use babel.

async function foo() {
  const res1 = await Redis.getAsync("boo")
  const res2 = await Redis.getAsync(res1)
}

answered Aug 31 '16 at 10:38

alex

5,467
4
33
43

How can I access properties from older then calls?

2 Answers2