Firebase realtime database + JS object

Question

I have a really simple JS code:

var worldRef = firebase.database().ref('something/something1');
var something = new Object();
worldRef.on('child_added', function(snap)  {
    something.id = snap.key;
    something.value = snap.val().value;
});
console.log(something);

It works almost fine - just one key&value from database, but it's something. If I modify it:

console.log(something.id);

Undefined. I've tried with map instead of object, but same. I see everything in map, but when I try to call the getmap(key), it's undefined.

Array-based solution:

var worldRef = firebase.database().ref('something/something1');
var something = [];
worldRef.on('child_added', function(snap)  {
  something.push ({
    id: snap.key,
    value: snap.val().value
  })
});
console.log(something);

It works.

What do you exactly mean by "console.log(something); works"? Can you pls show the exact output of this console.log as well as where you call it in your code? — Renaud Tarnec
– Renaud Tarnec, Commented Apr 25, 2020 at 14:57
Sure. I'm calling it right after the worldRef.on. The output: Object { } After I click on it: id: "US" value: 2373 — nervus
– nervus, Commented Apr 25, 2020 at 15:06
If I do it with curly braces, it's empty. Inside the function, all data is in my object. — nervus
– nervus, Commented Apr 25, 2020 at 15:11

Renaud Tarnec · Accepted Answer · 2020-04-25 15:58:40Z

1

This is because each time a child is added, you re-assign the id and value properties of your something object.

Since, the child_added event is triggered once for each initial child at this location (see the doc), at the end your object just contains the last children element.

If you do as follows (creating a new property for each child), you will see the same effect than with the Array:

var something = new Object();
worldRef.on('child_added', function (snap) {
   something[snap.key] = snap.val().value;
});

edited Apr 25, 2020 at 15:58

answered Apr 25, 2020 at 15:24

Renaud Tarnec

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6 Comments

Renaud Tarnec Over a year ago

Please share your entire code. As you have understood the result is highly dependent on the place of each element (in the callback, outside the callback, etc). Please add the code to your initial question, by editing it.

nervus Over a year ago

It works, but how should I use the key / value? something.key doesn't work, obviously. :/ So in your solution if I don't know what is the key, I can't use it.

nervus Over a year ago

Maybe a simple query is better, then the child_added?

Renaud Tarnec Over a year ago

You just have to take into account that the callback function is triggered several times (initially for each initial child at this location and then each time a new child is added). You have to adapt your object structure to follow this constraint.

Renaud Tarnec Over a year ago

"Maybe a simple query is better, then the child_added?" It's really difficult to say without knowing your full set of requirements and goal.

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