Data from a callback not storing on an array in js

Following is my code -

exports.saveWeekAvailability = function(req, res){
    console.log("-- SAVE WEEK WISE DATA --");

    weekData = req.body;
    var resultArr = [];
    for(var i=0; i< weekData.length; i++){
        Availability(weekData[i]).save(function(err, result){
            console.log("------------------------------------------");
            console.log(result);
            resultArr.push(result);
        });
    }
    console.log("-- Result Arr --");
    console.log(resultArr);

};

But every time resultArr is an empty array. Let me know what I am doing wrong here.

This is a duplicate. Check comments to your answer for duplicated post which contains a very good answer if you want to understand what is going on.

A quick solution for your problem:

for(var i=0; i< weekData.length; i++){
   (function(j) {
        Availability(weekData[i]).save(function(err, result){
            console.log("------------------------------------------");
            console.log(result);
            resultArr.push(result);
            if ( j == weekData.length - 1 ) {
                console.log("-- Result Arr --");
                console.log(resultArr);
            }
        });
    }(i));
}