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 }```
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
}
}
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)
}