Wait for a loop is finished JavaScript

Question

This is my code, I need to call callback only when the loop has reached its end.

function insertIntoCacheRange(userID, from, to, callback){
    var dataRanges = new Array();
    for(let pointer=from,  index = parseInt(from) + 1800 ; index < to; pointer+=1800, index +=1800){
        var count = 0;
        var sqlSelect = "SELECT count(*) as count FROM sensordata WHERE sensorid = ? AND time >= ? AND time < ?";
            con.query(sqlSelect, [userID, pointer, index], function(err, result){
                count = JSON.parse(JSON.stringify(result))[0].count;
                //console.log("pointer + " + pointer + " limit " + index + " = " +count);
                dataRanges.push(count);
                var sqlInsert = "INSERT INTO cache1800 (sensorid, time, count) VALUES(?,?,?)";
                con.query(sqlInsert, [userID, pointer, count],  function(err, result){
                    if(err) throw  err;

                });
            });      
    }
    callback(dataRanges);
}

Solved!! Finally I figure it out like this:

function insertIntoCacheRange(userID, from, to, callback){
    var dataRanges = new Array();
    for(let pointer=from,  index = parseInt(from) + 1800 ; index < to; pointer+=1800, index +=1800){
        var count = 0;
        var sqlSelect = "SELECT count(*) as count FROM sensordata WHERE sensorid = ? AND time >= ? AND time < ?";
            con.query(sqlSelect, [userID, pointer, index], function(err, result){
                count = JSON.parse(JSON.stringify(result))[0].count;
                //console.log("pointer + " + pointer + " limit " + index + " = " +count);
                dataRanges.push(count);
                var sqlInsert = "INSERT INTO cache1800 (sensorid, time, count) VALUES(?,?,?)";
                con.query(sqlInsert, [userID, pointer, count],  function(err, result){
                    if(err) throw  err;
                });
                //We reached the end of the loop (JS, you and your sync behaviour are crazy)
                if(dataRanges.length == 31){
                    callback(dataRanges);
                }
            });      
    }
}

I need to check if the array it's already 31 size. Then it's finished. Thank you very much for the idea :)

See: https://stackoverflow.com/a/43766002/157247 – T.J. Crowder Mar 31 '18 at 09:56 — T.J. Crowder, Mar 31 '18 at 09:56

score 1 · Accepted Answer · answered Mar 31 '18 at 09:59

You can check if the dataRanges length is equal or greater than number of possible iterations

function insertIntoCacheRange(userID, from, to, callback, errorCallback)
{
    var dataRanges = new Array();
    var numberOfIterations = (from-to)/1800; //find out number of possible iterations
    for(let pointer=from,  index = parseInt(from) + 1800 ; index < to; pointer+=1800, index +=1800){
        var count = 0;
        var sqlSelect = "SELECT count(*) as count FROM sensordata WHERE sensorid = ? AND time >= ? AND time < ?";
            con.query(sqlSelect, [userID, pointer, index], function(err, result){
                count = JSON.parse(JSON.stringify(result))[0].count;
                //console.log("pointer + " + pointer + " limit " + index + " = " +count);                 
                dataRanges.push(count);
                var sqlInsert = "INSERT INTO cache1800 (sensorid, time, count) VALUES(?,?,?)";
                con.query(sqlInsert, [userID, pointer, count],  function(err, result){
                    if(err) { errorCallback() }; //invoke error callback if there is an error                
                });
                //if dataRanges length has reached that value then callback
                if ( numberOfIterations <= dataRanges.length )
                {
                   callback(dataRanges);
                }
            });      
    }
}

Wait for a loop is finished JavaScript

1 Answers1