Node async await function execution not in order

Question

I'm confused. I'm new to async so I know I'm missing something fundamental but I'm scratching my head. From the examples I've seen, I thought I had this right but...

The below code works fine when mocked. However, when I fetch the real dashboard object from mongo I can see execution is not in order. Therefore the code that relies on there being a dashboard object fails due to it being 'undefined'.

Relevant code

router.get('/:id?', (req, res) => {
  getDashboardData(req)
})

async function getDashboardData(req) {  
  const dashboardId = await getDashboardId(req)
  const dashboard = await loadDashboard(dashboardId)
  const results = await showResults(dashboardId, dashboard)
}

async function getDashboardId(req) {
  dashboardId = req.params.id.trim()
  // Some other things happen here but ultimately we return a UUID 
  return(dashboardId)
}

async function loadDashboardFromId (dashboardId) {  
  Dashboard.findOne({dashboardId: dashboardId}).then((dashboard) => {
    if (dashboard == null || dashboard.dashboardId == null) {
      throw new Error('No dashboard matched in loadDashboardFromId for dashbardId: ' + dashboardId)
    } else {
      console.log('dashboard within loadDashboardFromId: ' + dashboard)
      return dashboard
    }      
  })
}

async function showResults(dashboardId, dashboard) {
  console.log("dashboardId: " + dashboardId)
  console.log("dashboard within showResults: " + dashboard)
}

Console output below. You can see showResults() executes before loadDashboard() returns:

connected to mongo server.
open connection to mongo server.
dashboardId: dbc7e954-c6a7-490f-8d9b-4dd11f11d262
dashboard within showResults: undefined
dashboard within loadDashboardFromId: {
  _id: new ObjectId("6208f552a442468c65987e62"),
  dashboardId: 'dbc7e954-c6a7-490f-8d9b-4dd11f11d262',
  createdDate: 2022-02-13T00:00:00.000Z,
  surveyId: 'b55a58d6-63f1-473e-9a3c-34f5d63af499',
  participantId: '9b274cfe-68ea-4206-9f3c-f2ee309ec4de',
  personalityTotal: new Decimal128("69"),
 // etc }```

Anatoly · Accepted Answer · 2022-02-13 20:16:14Z

2

Don't mix up then/catch and await. Use either one or another. I'd prefer await:

async function loadDashboardFromId (dashboardId) {  
  const dashboard = await Dashboard.findOne({dashboardId: dashboardId})
  if (dashboard == null || dashboard.dashboardId == null) {
    throw new Error('No dashboard matched in loadDashboardFromId for dashbardId: ' + dashboardId)
  } else {
    console.log('dashboard within loadDashboardFromId: ' + dashboard)
    return dashboard
  }      
}

edited Feb 13, 2022 at 20:16

answered Feb 13, 2022 at 17:49

Anatoly

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3 Comments

Chris Currie Over a year ago

This is making more sense now. Thanks @Anatoly. Any idea why I'm getting a comma moan? The 'const await dashboard = ' line has a comment " ',' expected".

Chris Currie Over a year ago

Seems in Node I needed a small tweak and everything is now working as planned. Appreciated. Change in syntax was: const dashboard = await Dashboard.findOne({dashboardId: dashboardId})

Anatoly Over a year ago

My bad. Misplaced await. I updated my answer

Khandker Ashik Mahmud · Accepted Answer · 2022-02-13 19:00:01Z

0

You can use Promise ... For More Documentation https://www.newline.co/fullstack-react/30-days-of-react/day-15/
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/resolve

  async function getDashboardData(req) { 
    var dashboardId;
    var dashboard;
    var promise = new Promise(async function(resolve, reject) {
      dashboardId = await getDashboardId(req)
      dashboard = await loadDashboard(dashboardId)
      if(dashboardId && dashboard){
         resolve(true);
       }
      })
    const results = await showResults(dashboardId, dashboard)
   }

edited Feb 13, 2022 at 19:00

answered Feb 13, 2022 at 17:55

Khandker Ashik Mahmud

1486 bronze badges

3 Comments

Chris Currie Over a year ago

I see, thanks. I got a syntax error warning as below. Any ideas? dashboardId = await getDashboardId(req) ^^^^^ SyntaxError: await is only valid in async functions and the top level bodies of modules

Khandker Ashik Mahmud Over a year ago

Oh i mistook it. I edited the code. new Promise(async function(resolve, reject) Here you use async. If you got error , Please comment here.

Anatoly Over a year ago

Oh, my! Why use new Promise inside async functions around two async function calls with await? Totally an overkill! They ARE already async and awaited there.

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