purposely throw error in a promise?

Question

How to purposely make a promise fail? Sometime I just skip the test and assume everything is fine, but I want to purposely make the promise to fail so that my catch is working.

exports.submitJob = async (req, res, next) => {
    const { cv } = req.body
    const userId = req.user._id

    try {

      if(!cv) {
        //how to pass error to catch block?
      }
      const save_submission = new Submission({
        userId,
        cv
      }).save()


    } catch(e => {
      res.json({
        status: 0,
        error: e
      })
    })

    next()
}

score 1 · Accepted Answer · answered May 19 '18 at 04:13

1

You can throw new Error('<your string here>');:

Note that catch is not something to be used with function syntax - the proper syntax is catch (e) { /* block that uses e */ }

const submitJobWhichWillFail = async (req, res, next) => {
  const cv = null;
  try {
    if (!cv) {
      throw new Error('cv must not be falsey!');
    }
    const save_submission = new Submission({
      userId,
      cv
    }).save()


  } catch (e) {
    console.log('res.json with error ' + e);
  }
}
submitJobWhichWillFail();

answered May 19 '18 at 04:13

CertainPerformance

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Why `throw('something is wrong')` also worked? i tried without the `new`, just `throw Error('something is wrong')` worked too. – Hoknimo May 19 '18 at 06:24
1

See [this answer](https://stackoverflow.com/questions/9156176/what-is-the-difference-between-throw-new-error-and-throw-someobject#answer-13016600) and the one below it - `throw new Error` is said to be more reliable, though it probably doesn't matter as much nowadays because more browsers are standards-compliant. – CertainPerformance May 19 '18 at 06:28

Martin Zeitler · Answer 2 · 2018-05-19T04:21:16.250

0

use the throw statement, maybe?

if(!cv) {throw("cv is absent");}

user-defined exception-types (alike one commonly has them in Java or PHP) are also possible and recommended, because one barely can differ the type by a string and otherwise can easily check the typeof the exception in the catch block. just learned from the MDN, that one eg. can also throw DOMException and Error.

edited May 19 '18 at 04:21

answered May 19 '18 at 04:10

Martin Zeitler

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purposely throw error in a promise?

2 Answers2