YANA_SENIUK-w1-UsingAPIs #37
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| number >= 10 && number <= 99 | ||
| ? resolve('This is a double digit number!') | ||
| : reject(new Error(`Expected a double digit number but got '${number}'`)); | ||
| }); |
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That's a nice use of the ternary operator here!
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| No, the problem does not occur with the promise-based version. | ||
| We have a better control of setTimeout, avoid callback hell, easier to read and scale | ||
| */ |
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While what you say is correct, it doesn't really explain the technical reason behind the change :)
When a promise rejects, it stops the execution of the function. So after reject is called on line 22, additional throws are not executed, and the loop stops there.
| The new promise resolves when all listed promises are resolved, and the array of their results becomes its result. | ||
| Promise.all never stop promises. This method return promise which was rejected or all all promises are resolved and return their results. | ||
| Other promises are still running, cause if it was started it will continue till resolve or rejected state. | ||
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| Promise.All just ignores their result in this case. |
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I think you got it right, although you chose a somewhat roundabout way to explain it. It could also be summarized as:
- Each
rollDie(number)function is an independent async process. Promise.all()does not cancel any promises; it just waits.- So even if one promise rejects, the rest keep going.
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Your solution is good, and the benefit is that it's easy to understand what's happening or troubleshoot. On the other hand, it includes some code repetition and would be harder to scale if you had a larger number of dice to throw.
If you wanted to streamline the code, you could define a function factory that returns a new .then() handler for each die, capturing the die number in a closure.
const pushAndRoll = (dice) => (value) => {
results.push(value);
return rollDie(dice);
};
Then, you could do:
[...]
return rollDie(1)
.then(pushAndRoll(2))
.then(pushAndRoll(3))
.then(pushAndRoll(4))
.then(pushAndRoll(5))
.then((value) => {
results.push(value);
return results;
});
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