Array.length equals 0 always

Question

I'm trying to get the length of my array, but I always getting 0 even when the console show that I push 5 objets

async function getDiaries() {
 return new Promise((resolve, reject) => {
  var url = firebase.database().ref('/diary');
  var diaries = [];
  url.on('value', (snap) => {
    snap.forEach((child) => {
        diaries.push({
          key: child.key,
          name: child.val().name,
          date: child.val().description,
          url: child.val().url,
          idOwner: child.val().idOwner
        });
    });
});
console.log(diaries.length);// get 0
resolve(diaries)
})}

This is what the console shows me

You are printing before your array gets filled... you are misleading in async concepts — guijob, Jul 24 '17 at 06:38

score 1 · Answer 1 · answered Jul 24 '17 at 06:38

1

Move the console.log into your callback function, otherwise it will mostly always run before your callback is executed. In other words: you get a 0 because the length is 0 at this point.

answered Jul 24 '17 at 06:38

Rob

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score 1 · Answer 2 · answered Jul 24 '17 at 06:39

Ofcourse you will get this 0 because this is async function you can try like that

async function getDiaries() {
 return new Promise((resolve, reject) => {
  var url = firebase.database().ref('/diary');
  var diaries = [];
  url.on('value', (snap) => {
    snap.forEach((child) => {
        diaries.push({
          key: child.key,
          name: child.val().name,
          date: child.val().description,
          url: child.val().url,
          idOwner: child.val().idOwner
        });
    });
    console.log(diaries.length);
    resolve(diaries);
});
})}

score 1 · Accepted Answer · answered Jul 24 '17 at 06:39

url.on is likely asynchronous, meaning you need to do the console.log inside the callback:

async function getDiaries() {
  return new Promise((resolve, reject) => {
    var url = firebase.database().ref('/diary');
    var diaries = [];
    url.on('value', (snap) => {
      snap.forEach((child) => {
        diaries.push({
          key: child.key,
          name: child.val().name,
          date: child.val().description,
          url: child.val().url,
          idOwner: child.val().idOwner
        });
      });
      console.log(diaries.length); // get 0
      resolve(diaries);
    });
  });
}

Thank you so much! , i'm not a master controlling the asynchronous functions, is hard to get the core idea — Mario Villalobos, Jul 25 '17 at 20:03

Array.length equals 0 always

3 Answers3