Firebase - save query to an object/map/array in JS

Question

I have a firebase realtime database. I would like to write a query and save the data to an array and work with later. Can I do it somehow? This code works nicely, just need to save it somehow for later. Object / map would be great, but an array works too. My half-code is here:

map = new Map();
var rootRef = firebase.database().ref("locations/map");
rootRef.once("value", function(snapshot) {
  snapshot.forEach(function(child) {
    console.log(child.key+": "+child.val().value);
    map.set(child.key, child.val().value);
  });
});
console.log(map);

It works fine, but if i try

console.log(map.get(0));

It's undefined. It's need to this for:

 for (i = 0; i < someaarray.data.length; i++) {
  if (someaarray.data[i].id == map.get(id))
  {
    someaarray.data[i].value = map.get(value);
  }
}

Peter Haddad · Accepted Answer · 2020-04-25 20:14:43Z

1

You need to return a promise since the fetching data is asynchronous, therefore try the following:

function getData() {
return new Promise((resolve, reject) => {
let map = new Map();
var rootRef = firebase.database().ref("locations/map");
rootRef.on("value", function(snapshot) {
  snapshot.forEach(function(child) {
    console.log(child.key+": "+child.val().value);
    map.set(child.key, child.val().value);
    resolve(map);
   });
  });
 });
}

Then when you need to use the map, you need to do the following:

getData().then((value) => {
  console.log(value.get(0));
 });
});

Check here for more info:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then

answered Apr 25, 2020 at 20:14

Peter Haddad

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2 Comments

nervus Over a year ago

Thanks! I've tried your code, but the "console.log(value.get(0));" is undefined. :(

Peter Haddad Over a year ago

is child.key equal to 0? Because inside get() you need to write the key. Do console.log(value)

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