Secondary Sort

I have an array of objects. My object definition is given below:

function tempArray(code,height,weight)
{
this.code = code;
this.height = height;
this.weight = weight;
}

I used the following function to sort.

function sortBy(prop,arr) {
sortProp=prop;
arr=arr.sort(sortFunc);
}


function sortFunc(part1,part2) {
if (part1[sortProp]>part2[sortProp]) retVal=-1;
else if (part1[sortProp]<part2[sortProp]) retVal=1;
else retVal=0;
return retVal;
}

This however allows me to sort only by one criteria. I need to sort by
weight first and then by height for those items that have the same
weight.