SOURCE

var str = '1,2,1,3,2,3,3,4,5,6';
var arr = str.split(',');
var l = arr.length / 2;
var jsonarr = [];
console.log(l);
for(var i = 0; i < l; i++){
    //var a = new Object();
    //a.lat = arr[i];
    //a.lan = arr[i+1];
    var a = [];
    a[0] = arr[i];
    a[1] = arr[i+ 1]; 
    jsonarr.push(a);
}

console.log(jsonarr);