AsyncAwaitTest

This project demonstrates the async-await TS transform and associated awaiter function as implemented in the following PRs:

The project is based on and built with the Angular CLI; although there is no actual Angular application code here. It has been configured to only produce "development" mode output. In other words optimisations like minification have been turned off.

Instructions

Install the dependencies: npm install.

There is a postinstall hook to turn off the CLI downleveling of async-await. You can manually turn this transform on and off using npm run turn-on-cli-transform and npm run turn-off-cli-transform.

Run the app code

Run and serve the app: npm start.

Run the test code

The CLI is not able to run the TS transform for the unit tests, so these are run using jasmine on node.js:

Compile and run the tests: npm test.

Build the app code

The distributabe code can be build using npm run build. The output can be found at dist.

What to look for

The application main.ts copies the code from the "async vs promise" jsfiddle, which executes recursive async functions; and also demonstrates a chain of native async functions.

The output demonstrates what the stack traces look like for each case:

main.ts:23 promise pn(5)
main.ts:23 promise pn(4)
main.ts:23 promise pn(3)
main.ts:23 promise pn(2)
main.ts:23 promise pn(1)
main.ts:23 promise pn(0)
main.ts:34 promise pn().catch()
main.ts:35 Error: ouch pn
    at main.ts:27
    at _ZoneDelegate.invoke (zone.js:378)
    at Zone.run (zone.js:140)
    at zone.js:1286
    at _ZoneDelegate.invokeTask (zone.js:412)
    at Zone.runTask (zone.js:184)
    at drainMicroTaskQueue (zone.js:591)

async fn() 5
main.ts:7 async fn(4)
main.ts:7 async fn(3)
main.ts:7 async fn(2)
main.ts:7 async fn(1)
main.ts:7 async fn(0)
main.ts:15 async fn().catch()
main.ts:16 Error: ouch
    at fn_generator (main.ts:10)
    at fn_generator.next (<anonymous>)
    at Function.Zone.__awaiter (zone.awaiter.js:18)
    at async Function.Zone.__awaiter (zone.awaiter.js:19)
    at async Function.Zone.__awaiter (zone.awaiter.js:19)
    at async Function.Zone.__awaiter (zone.awaiter.js:19)
    at async Function.Zone.__awaiter (zone.awaiter.js:19)
    at async Function.Zone.__awaiter (zone.awaiter.js:19)

main.ts:58 p1().catch()
main.ts:59 Error: BOOM
    at p4_generator (main.ts:54)
    at p4_generator.next (<anonymous>)
    at Function.Zone.__awaiter (zone.awaiter.js:18)
    at p4 (main.ts:53)
    at p3_generator (main.ts:50)
    at p3_generator.next (<anonymous>)
    at Function.Zone.__awaiter (zone.awaiter.js:18)
    at p3 (main.ts:49)
    at p2_generator (main.ts:46)
    at p2_generator.next (<anonymous>)

Note that in the recursive native async case the stack trace is not particularly helpful. When viewed in the debuger the stack trace is more accurate. Could this be a problem with how the v8 engine optmizes these calls?

In the third case, it is possible to see the actual call stack down to the p4() that throws.

petebacondarwin / async-await-test