Promise.catch() not catching errors from promise

Question

I'm trying to check a number of conditions, and if one of them is true I want to proceed to a certain callback function. Otherwise, I want to proceed to a different callback function. Some pseudocode might look like:

if (condition_1 OR condition_2 OR condition_3) {
    on_satisfied()
} else {
    on_unsatisfied()
}

However, checking each of these conditions takes a while (for example, it may require a database query), so I want to check them asynchronously. I also know that if any one of them returns TRUE, I have already satisfied my condition and thus want to stop execution and forget about the remaining conditions. In hopes of doing that, I wanted to use the "dirty trick" described here in the first response: throwing an error that will be handled within a parent function (which is inside a promise here)

// the function we call if at least one condition is satisfied
function on_satisfied() {
    console.log("At least one condition satisfied")
}

// the function we call if no conditions are satisfied
function on_unsatisfied() {
    console.log("No conditions satisfied")
}

// a sample condition-checking function
async function check_lessthan_5(to_check, callback_if_not) {
    // using a timeout to simulate "slow" checking of conditions;
    // the slow checking could be a result of e.g. database queries
    await new Promise(r => setTimeout(r, 2000));
    if (to_check < 5) {
        // throw this error in hopes of terminating parent function,
        // because it is sufficient for one condition to be met 
        // in order for the whole OR-joined expression to be true (we want to stop execution of the parent function)
        throw Error("value < 5")
    }
    return false
}

const all_cond_checker = new Promise((resolve, reject) => {
    // store all the resulting promises, 
    // so when they all resolve we know that no conditions were satisfied
    var conditions_list = []
    // check all the conditions. In this case, we want to see if any of these numbers is >= 5
    for (var i=0; i < 10; ++i) {
        // push a resulting promise into the list, we can check later that it resolves
        // if the condition is met, terminate this function by propagating error up
        conditions_list.push(check_lessthan_5(i)).catch((error) => {resolve()})
    }
    // once all the promises return, us getting here implies no errors were thrown 
    // which implies no conditions satisfied
    Promise.all(conditions_list).then(reject)
});

The problem is that it seems like the .catch() inside the promise does not catch the error! Running the code, I get the following:

$ node async_test.js
No conditions satisfied
/home/daniel/Signoff-again/node-experiments/async_test.js:20
            throw Error("value >= 5")
            ^

Error: value < 5
    at Timeout._onTimeout (/home/daniel/Signoff-again/node-experiments/async_test.js:20:19)
    at listOnTimeout (node:internal/timers:557:17)
    at processTimers (node:internal/timers:500:7)

My interpretation of these results is that, for some reason, the .catch() is totally skipped, the error is unhandled, the for-loop is broken, then the Promise.all() is executed (because all 5 of the Promises in conditions_list have been resolved) and so the on_unsatisfied function is called. Instead, what I would want/expect is for the on_satisfied function to be called as soon as the first check_lessthan_5 returns.

So the question: why is it happening that the catch() seems not to work here? Also, is there a better way of doing this?

Thanks in advance.

I expect that as soon as the first condition is satisfied, the returned error is caught by the .catch() in all_cond_checker and then on_satisfied is called. I do not expect the error to propagate all the way "out" and be reported in the console.

The expected console output is:

$ node async_test.js
At least one condition satisfied

Answer 1

You have the catch in the wrong place

async function check_lessthan_5(to_check) {
  await new Promise((r) => setTimeout(r, 2000));
  if (to_check < 5) {
    throw Error('value < 5');
  }
  return false;
}

const all_cond_checker = new Promise((resolve, reject) => {
  var conditions_list = [];
  for (var i = 0; i < 10; ++i) {
    conditions_list.push(check_lessthan_5(i));
  }
  Promise.all(conditions_list)
    .then((r) => resolve(r))
    .catch((err) => reject(err));
});

all_cond_checker
  .then((r) => console.log(r))
  .catch((err) => console.log(err.message));