I'm trying to create a function that check if mooving bullet is hitting players.
The code simplified - shoot() is moving the bullet, and check_if_bullet_hit_player(bulletRef) gets a bullet ref, and checks if the bullet is hitting any player.
This is my code:
function shoot(){
// ... moving bullet code
const bulletRef = firebase.database().ref(`bullets/${bulletKey}`);
if(check_if_bullet_hit_player(bulletRef)){
alert("player got hit");
bulletRef.remove();
}
}
function check_if_bullet_hit_player(bulletRef){
bulletRef.once("value").then(function(snapshot) {
//for simplicity I just return true - player got hit
return true;
}
}
The code is not triggering the alert(). After reading this question I think the problem with the asynchrony, but how do I pass parameters to the function, and get the function's return value.
This is the full check_if_bullet_hit_player() function, which I loop over the players, and checks if the bullet is <0.5 to a player (if so - its count as a hit):
function check_if_bullet_hit_player(bulletRef){
//bulletRef.once("value").then(function(snapshot) {
return bulletRef.get().then(snapshot => {
let bulletX = snapshot.val().x;
let bulletY = snapshot.val().y;
let shooterId = snapshot.val().shooterId;
//loop over players
const allPlayersRef = firebase.database().ref(`players`);
allPlayersRef.once("value", (snapshot) => {
players = snapshot.val() || {};
Object.keys(players).forEach((key) => {
if(getDistance(players[key].x, players[key].y, bulletX, bulletY) < 0.5){
if(players[key].id != shooterId){ //not the shooter
return true;
}
// ...
Indeed the problem comes from the fact the once() method is asynchronous. But you also forget to return the promises chain in the check_if_bullet_hit_player() function.
The following, using then() as you do in your question, should do the trick:
function shoot() {
// ... moving bullet code
const bulletRef = firebase.database().ref(`bullets/${bulletKey}`);
check_if_bullet_hit_player(bulletRef)
.then(result => {
if (result)
bulletRef.remove();
})
}
function check_if_bullet_hit_player(bulletRef) {
return bulletRef.get().then(snapshot => { // See return at the beginning, and also that we use get()
return snapshot.exists(); // I think you should check if the snapshot exists
});
}
Note that the shoot() function is also asynchronous. So if you chain it with other function call, you need to use then() (and return the promises chain) or async/await.
Edit following your comment and your question update:
Again you are not returning the promise chain. You can modify it as follows, but I would recommend you use the every() method which "executes the provided callback function once for each element present in the array until it finds the one where callback returns a falsy value"
function check_if_bullet_hit_player(bulletRef) {
let bulletX;
let bulletY;
let shooterId;
return bulletRef.get().then(snapshot => {
bulletX = snapshot.val().x;
bulletY = snapshot.val().y;
shooterId = snapshot.val().shooterId;
//loop over players
const allPlayersRef = firebase.database().ref(`players`);
return allPlayersRef.get(); // HERE we chain the promise
})
.then(allPlayersSnap => {
players = allPlayersSnap.val() || {};
let result = false;
Object.keys(players).forEach((key) => {
if (getDistance(players[key].x, players[key].y, bulletX, bulletY) < 0.5 && players[key].id != shooterId) {
result = true;
}
});
return result;
});
}
It seems these functions are executed in the front end (you use firebase.database()...) You should probably do the calculations in the back-end, e.g. via a Cloud Function, to avoid possibilities for a malicious user to fake the results.