var binarySearch = function(dataArr, target, start, end) {
var middle;
//robustness,预防没有指定起始位置
if (start == null) {
start = 0;
}
if (end == null) {
end = dataArr.length - 1;
}
middle = parseInt((start + end) / 2);
//查找结束判定条件
if (middle === start || middle === end) {
return -1;
}
if (dataArr[middle] === target) {
return middle;
}
if (target < dataArr[middle]) {
return binarySearch(dataArr, target, 0, middle - 1);
} else {
return binarySearch(dataArr, target, middle + 1, end);
}
};