带有承诺的承诺链上的“未处理的承诺拒绝”

Question

I'm getting the exception:

(node:1356) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Cannot edit expense on issued invoice

My code uses a promise chain to update some data. It gets the database version first using getExpense , then checks the user is allowed to edit it (it's not been issued ). If it has been issued, it rejects the promise, if not it continues to perform update , then get the updated data using getExpense again in order to return it.

However, when running with an 'issued' expense, the update goes through and there's the above error. Rejection with the message "Cannot edit expense on issued invoice" is expected, but why is it not being caught?:

  expensesModels.getExpense(expense.id)
    .then(validatedExpense => {
      if (validatedExpense.issued) {
        Promise.reject('Cannot edit expense on issued invoice');
      } else {
        Promise.resolve();
      }
    })
    .then(() => expensesModels.update(expense))
    .then(() => expensesModels.getExpense(expense.id))
    .then(returnExpense => response.json(returnExpense))
    .catch(err => errorHandling.onError(err, response));

I understand that this error is caused when there's not a catch terminating the promise chain, but I'm catching in order to reject the HTTP request in the last line.

Answer 1

您不必返回Promise.reject从你的第一个.then 。

Answer 2

To continue down the 'then' chain, 'promise.resolve()' is called on the returned value.

Since your first then function does not return the 'promise.reject()', 'promise.resolve()' is treated as the return value and the chain progresses without the error being caught.