Firebase Return Output From Function

I am new in firebase and I'm trying to pass a $variable in a function to check if the $variable is exists. function ifExistWaybillNo(waybill_no) { var databaseRef = firebase.data

Solution 1:

Almost everything Firebase does is asynchronous. When you call the function ifExistWaybillNo it expects an immediate return, not to wait. So before your databaseRef.orderByChild("waybill_no") is finished the statement that called the function has already decided the return is undefined.

The way to fix this is by passing a callback function and using the return there. An exact explanation of this is done very well here: return async call.

You just need to rename some of the functions and follow syntax used there.

To start:

function(waybill_no, callback) { 
    databaseRef.orderByChild("waybill_no").equalTo(waybill_no).on('value', function(snapshot) {
    var truth = snapshot.exists();
    callback(truth); // this will "return" your value to the original caller
  });
}

Remember, almost everything Firebase is asynchronous.