var myArray2 =[];
    myArray2[10]='x';
    myArray2[55]='x';

Array.prototype.trueLength= function(){
    for(var i = 0,ctr=0,len=myArray2.length;i<len;i++){
        if(myArray2[i]!=undefined){
            ctr++;
        }
    }
    return ctr;
}
console.log(myArray2.trueLength());

var length = myArray2.reduce(function(sum) {
    return sum+1;
}, 0);

var length = myArray2.filter(function(item, idx) {
    return idx in myArray2;
}).length;

Object.keys(myArray2).length;

for (var length = 0, i = 0; i < myArray2.length; i++) {
    if (i in myArray2) {
        length += 1;
    }
}

Array.prototype.trueLength= function(){
  var ctr = 0;
  for(var i in this){
        if(this.hasOwnProperty(i)){
            ctr++;
        }
    }
    return ctr;
}
console.log(myArray2.trueLength());

Array.prototype.trueLength= function(){
    var list= [], ctr = 0, array = this;

    for(var i in array) (function(arr) {

        if(array.hasOwnProperty(i)){
            list.push(arr);
            ctr++;
        };


    }(array[i]));

    return {length: ctr, "list": list}
}

var myArray2 =[];
    myArray2[10]='44';
    myArray2[55]='55';

// list not undefined
myArray2.trueLength().list  // ["44", "55"]

// not undefined length list
myArray2.trueLength().length // 2

function getArrayPropertyCount(arr) {
    var count = 0;
    for (var i = 0, len = arr.length; i < len; ++i) {
        if (i in arr) {
            ++count;
        }
    }
    return count;
}