Async function not waiting long enough to push firestore docs into an array

Question

I am trying to get a bunch (10-1500) of documents from firestore and then once I have them I check the amount I got, and then handle it from there.

I can only get this to work when I have a manual 'setTimeout' in between grabbing the docs and checking the array.

The array is not being filled with all of the firestore documents before I check for them but it is in an async function so I am confused to why it isn't waiting.

this is not a firestore issue, I receive all of the documents as I expect.

javascript async function

async function query(units, days){

  try {

    let allLogs = []

    var ts = moment().subtract(days,'days').valueOf() //ms timestamp from 1 -3 days ago


       await units.forEach(async(e) => {

         let ref = db.collection('units').doc(`${e.unit.superId}`).collection('logs').where('info.ms', '>=', parseInt(ts))

         let docs = await ref.get()  // get all subcollection documents from parent document

          await docs.forEach(async(doc) =>{ // Loop through and push all documents to allLogs array

             allLogs.push(doc.data())

           })
       })


     //If i dont add this: it will always think allLogs is empty. Not waiting long enough for it to be filled

     await new Promise(resolve => setTimeout(resolve, (days+ 1.5) * 1000 )); // x seconds wait for array to be filled


     if (allLogs.length > 0){
       console.log('filled')
     } else {
      console.log('empty')

     }


  } catch(err) {

    console.log(err)
  }


}

DontBreakAlex · Accepted Answer · 2021-03-01 20:51:29Z

2

forEach does not await callbacks

It fires all calls sequentially and does not await them (it also return undefined, so awaiting it does nothing)

Use a for ... of loop to await each call

for (const unit of units) {
    let ref = db.collection('units').doc(`${unit.unit.superId}`).collection('logs').where('info.ms', '>=', parseInt(ts))
    let docs = await ref.get() // get all subcollection documents from parent document
    docs.forEach((doc) => { // Loop through and push all documents to allLogs array
        allLogs.push(doc.data())
    }
}

Or fire all promises and await all of them with Promise.all

await Promise.all(units.map(async (unit) => {
    let ref = db.collection('units').doc(`${unit.unit.superId}`).collection('logs').where('info.ms', '>=', parseInt(ts))
    let docs = await ref.get()  // get all subcollection documents from parent document
    docs.forEach((doc) => { // Loop through and push all documents to allLogs array
        allLogs.push(doc.data())
    })
}))

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all

answered Mar 1, 2021 at 20:51

DontBreakAlex

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1 Comment

Maulik Over a year ago

you just save my day : ) i was trying forEach() function but i now i realize to use for of function. agian very useful answer

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