Decorator descriptor is missing

I have issue with using vue-jest along with typescript decorators. Decorator method is not receiving 3rd parameter called descriptor. TS docs: https://www.typescriptlang.org/docs/handbook/decorators.html

Runnable reproduction: https://github.com/budziam/vue-decorator-issue I have created two almost identical components.

• Example1 - component created in .vue file
• Example2 - component created in .ts file

Example 1 and 2 both have one decorated method. When you mount the component there is difference in 3rd parametr received by the decorator function. In Example1 case we get undefined while in Example2 we get appropriate object.

You can reproduce it by running

$ yarn test
yarn run v1.17.3
$ jest
 PASS  __tests__/mount.test.ts
  ✓ mount component from vue file (9ms)
  ✓ mount component from ts file (2ms)

  console.log src/decorator.ts:2
    { target:
       Example1 { constructor: [Function: Example1], action1: [Function] },
      key: 'action1',
      descriptor: undefined }

  console.log src/decorator.ts:2
    { target:
       Example2 { constructor: [Function: Example2], action2: [Function] },
      key: 'action2',
      descriptor:
       { value: [Function],
         writable: true,
         enumerable: true,
         configurable: true } }

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        1.094s
Ran all test suites.
Done in 1.58s.

My real-case scenario is using @Emit decorator from vue-property-decorator library. When I bundle my code using webpack, everything is OK. However, an error occurs when running tests

TypeError: Cannot read property 'value' of undefined

It happens because descriptor is undefined.

[vanhoofmaarten]

Ok, because I wasn’t clearing the Jest cache, it generated false positives of which I provided you as a solution. My apologies.

vue-jest does pick up the correct tsConfig, so no need for the extra globals configuration.

However, I believe to get the correct decorator transformation, you need to set the compilerOptions.target to esnext.

I tested this approach multiple times with success by running the following commands.

jest --clearCache
jest

I would love to provide you with a more clear answer why this works, but I haven’t really figured out the how and why yet.

I believe it has something to do with the update on the TC39 Decorator proposal

Hopefully, this will solve your problem.

[vanhoofmaarten]

My pleasure!