javascript - Firebase return output from function -


i new in firebase , i'm trying pass $variable in function check if $variable exists.

function ifexistwaybillno(waybill_no) {   var databaseref = firebase.database().ref('masterlist');   databaseref.orderbychild("waybill_no").equalto(waybill_no).on('value', function(snapshot){     alert(snapshot.exists()); //alert true or false   }); }

the above function work's fine when changed alert(snapshot.exists()); return snapshot.exists(); doesn't working. return undefined, should return true or false.

how can this? in advance

almost firebase asynchronous. when call function ifexistwaybillno expects immediate return, not wait. before databaseref.orderbychild("waybill_no") finished statement called function has decided return undefined.

the way fix passing callback function , using return there. exact explanation of done here: return async call.

you need rename of functions , 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); // "return" value original caller   }); }

remember, firebase asynchronous.


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