JavaScript array not iterable
If posts is an iterable I would look into using some version of q.all and then when all promises are resolved you can reliably log the result of push all those pieces into the statuses array.
some pseudo code:
if (user) {
app.props.fb.database().ref(`/users/${user.uid}/timeline`)
.once('value')
.then(snapshot => snapshot.val())
.then(posts => {
const statuses = [];
const promises = Object.keys(posts).map(key => {
return app.props.fb.database().ref(`/posts/${posts[key]}`).once('value')
.then(snapshot => statuses.push(snapshot.val()));
}
return Promises.all(promises)
})
.then(() => console.log(statuses));
}
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hackerman
Updated on June 04, 2022Comments
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hackerman almost 2 years
I hit a really weird issue with a simple JavaScript array last night. I am working on a React Native app powered by Firebase and getting data from the real-time database with the SDK.
Here is the code:
var app = this this.props.fb.auth().onAuthStateChanged(function(user) { if (user) { app.props.fb.database().ref('/users/' + user.uid + "/timeline").once('value').then(function(snapshot) { var posts = snapshot.val() return posts }).then((posts) => { var statuses = []; for (i in posts) { app.props.fb.database().ref('/posts/' + posts[i]).once('value').then(function(snapshot) { statuses.push(snapshot.val()) }); } console.log(statuses) }) } });
The above code is supposed to get the data from the
timeline
of each user, iterate through each of theposts
on thetimeline
and then get the data of the post fromposts
. It then simply pushes the data to thestatuses
array, which is being console logged at the end.This is what shows up on the console.
Until the array is expanded, the console doesn't show the items in the array. Additionally, when I try to get the
length
of the array, it returns 0 and I also can't iterate through the items on the array.What am I doing wrong?
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Sten Muchow over 6 years99/100 JS errors seem to be async issues - this looks the same. u cannot log in the console an array that is being populated by an async call.
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Phylogenesis over 6 yearsYou shouldn't iterate an array using a
for..in
construct. UseArray.prototype.forEach()
.
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hackerman over 6 yearsHow would that work? I am kinda new to this so would be really helpful if you could show me an example
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Sten Muchow over 6 yearsthere ya go... seems we have Promises.all to work with -> developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…
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hackerman over 6 yearsThank you so much!
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Sten Muchow over 6 yearsI added some es6-ification of your code as well, makes it a bit sexier with template strings, arrows functions, auto return statements ;)
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hackerman over 6 yearsNeat stuff! Thanks again :)