Issue with adding numbers to an array element and assigning to another array element

Question

In my code below, in the line ipClassRangeTop[3] = ipClassRangeBottom[3] + subNetCount - 1; it seems that the subNetCount is also added to the ipClassRangeBottom[3] as well. This is not the result I was expecting. I just want the ipClassRangeTop[3] to have that value.

Could someone people let me know what I may be doing wrong. I am very new to any type of coding so any help would be very appreciated.

var ipAddress = "172.16.1.1";
var subNetCount = 1 << 6;
var ipClassRangeTop = new Array();
var ipClassRangeBottom = new Array();
var classMaskDec = 65536;
var loopCount = 3; //classMaskDec/subNetCount;

//console.log(ipAddress, "ip address");
ipAddress = ipAddress.split(".");
ipClassRangeBottom = ipAddress;
ipClassRangeBottom[2] = 0;
ipClassRangeBottom[3] = 0;
ipClassRangeTop = ipClassRangeBottom;
//console.log(ipAddress, "ip address");

while (loopCount > 0 ) {
//console.log(i++);
console.log(ipClassRangeBottom, "1st bottom in loop");

ipClassRangeTop[3] = ipClassRangeBottom[3] + subNetCount - 1;
console.log(ipClassRangeBottom, "after top [3] assign");

if (ipClassRangeTop[3] > 255) {
    ipClassRangeTop[2] = ipClassRangeTop[2] + 1;
    ipClassRangeTop[3] = subNetCount - 1;
    console.log("IF RAN");
}

console.log(loopCount);
console.log(ipClassRangeTop);
console.log(ipClassRangeBottom);

ipClassRangeBottom[3] = ipClassRangeBottom[3] + subNetCount;
console.log(ipClassRangeBottom);
loopCount--;
}

console.log(ipAddress, "ip address");
console.log(ipClassRangeTop);
console.log(ipClassRangeBottom);

Thanks, Mark

Pointy · Accepted Answer · 2013-06-24 02:03:57Z

4

Assigning a reference to an array from one variable to another does not make a copy of the array (in JavaScript). That is:

var a = [1, 2, 3];
var b = a;
b[0] = "Hello World!";
alert(a[0]); // alerts "Hello World!"

If you want to make a real copy of an array:

var a = [1, 2, 3];
var b = a.slice(0);
b[0] = "Hello World!";
alert(a[0]); // alerts "1"

answered Jun 24, 2013 at 2:03

Pointy

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