compare different arrays with mapping field

// source CSV
var first=JSON.parse('[{"a":"one","b":"123","c":"567"},{"a":"two","b":"2"},{"a":"six","b":"2"},{"a":"three","b":"3"}]');

// source API
var second=JSON.parse('[{"a":"one","b":"1"},{"a":"ten","b":"2"},{"a":"three","b":"3"}]');

// records which deos not exist in API will put in newContent
var newContent = [];

// a temporary row to transfer an unexisting antry to newContent
var row = [];

// default assumtion is that all records from CSV exist in API
var exists=0;

// the outcome array. A merged data from CSV and API
var alltogether = [];

// iterate through CSV
for (i in first) {
// so far the line has been not found
        //
// by default let's assume the line is there
exists=0;
        // go through other array
        for (j in second) {
                // compare value
                if (first[i].a === second[j].a) {
                exists=1;
                row = second[j];
                Zabbix.Log(4,"existing="+JSON.stringify(row));
                // if value exists then imediatelly stop the itereation to save some performance
                break;
                }
        }

// if the previous loop failed to enable flag 'exists=1', it's crear indication the value does not exist in API
if (exists===0) {
        Zabbix.Log(4,'"'+first[i].a+'" does not exist in second array');
        // here we need to hardcode every line
        newContent.push({"a":first[i].a,"b":"new"});
}

}

// merge the existing API array together with the content which does not exist in API
for (el in second) alltogether.push(second[el]);
for (el in newContent) alltogether.push(newContent[el]);

return JSON.stringify({
  'first': first,
  'second': second,
'alltogether': alltogether
});