I am trying to return an array of pushed data from promise, then loop multiple times to populate all data. For instance, I got a list of brands and a function to take in brand parameter and return an array of pushed data.
var datasetarr = [];
brandlist = ['Bh', 'Ruffles'];
let promiseKey = new Promise((resolve, reject) => {
for(var i = 0; i < brandlist.length; i++){
datasetarr = populateData(brandlist[i], datasetarr);
}
resolve(datasetarr);
});
promiseKey.then((arr) => {
console.log('complete promise');
for(var i = 0; i < arr.length; i++){
console.log(arr[i].date + ' ' + arr[i].total);
}
});
The error message is
Uncaught (in promise) TypeError: Cannot read property 'length' of undefined
at promiseKey.then
My data fetching has no problem as I managed to print out the details. This means that the promise is not resolve properly. Is that the correct way to return an array from promise? I not sure which part was wrong.
Firstly, your populateData needs to return a Promise - in this case, it would be the resolved array of promises created in data.forEach
var brandlist = ['Bh', 'Ruffles'];
let promiseKey = Promise.all(brandlist.map(brand => populateData(brand)))
.then(results => [].concat(...results)); // flatten the array of arrays
promiseKey.then((arr) => {
console.log('complete promise');
for(var i = 0; i < arr.length; i++){
console.log(arr[i].date + ' ' + arr[i].total);
}
});
function populateData(brand, datasetarr) {
console.log('go in');
var query;// = // query by brand parameter
return query.once('value').then(data => {
var promises = [];
data.forEach(snapshot => {
// get each receipt item details
// get receipt details by receipt ID
var query;// = // query receipts
promises.push(query.once('value').then(data => {
// removed code
// managed to print out here so data fetching is not a problem
console.log(brand + ' ' + date + ' ' + itemTotal);
return {date: date, total: itemTotal};
}));
});
return Promise.all(promises);
});
}
Or, using the snapshotToArray function I gave you in this answer a week ago
const snapshotToArray = snapshot => {
const ret = [];
snapshot.forEach(childSnapshot => {
ret.push(childSnapshot);
});
return ret;
};
function populateData(brand, datasetarr) {
console.log('go in');
var query;// = // query by brand parameter
return query.once('value').then(data => Promise.all(snapshotToArray(data).map(snapshot => {
// get each receipt item details
// get receipt details by receipt ID
var query;// = // query receipts
return query.once('value').then(data => {
// removed code
// managed to print out here so data fetching is not a problem
console.log(brand + ' ' + date + ' ' + itemTotal);
return {date: date, total: itemTotal};
});
})));
}
While it's possible to work with a global datasetarray variable to which you push from anywhere, I would recommend against it. Instead, write a method getData that returns (a promise for) an array, and after calling that multiple times (once for every brand) you concatenate them together.
const brandlist = ['Bh', 'Ruffles'];
const promiseKey = Promise.all(brandlist.map(getData)).then(arrays => [].concat(...arrays));
promiseKey.then(arr => {
console.log('complete promise');
for (const item of arr)
console.log(item.date + ' ' + item.total);
});
function getData(brand) { // no array parameter!
console.log('go in');
const query = …; // query by brand parameter
return query.once('value').then(data => {
const promises = toArray(data).map(snapshot => {
const query = …; // get receipt item details by receipt ID
return query.once('value').then(data => {
…
return {date: date, total: itemTotal}; // don't push, just return the result
});
return Promise.all(promises); // resolves with an array of results
}); // resolves with that same result array
}
function toArray(forEachable) {
const arr = [];
forEachable.forEach(x => { arr.push(x); });
return arr;
}
