var binarySearch = function(arr, record){
	var start = 0;
	var end = arr.length -1;

	var middleIndex;
	var firstIndex = -1;

	while(start <= end){
		if( start === end){
			middleIndex = start;
		}else{
			// end + start may overflow
			middleIndex = Math.floor((end - start) / 2) + start;
		}

		if(arr[middleIndex] === record){
			firstIndex = middleIndex;
			end = middleIndex -1;
		}else if(arr[middleIndex] > record){
			end = middleIndex - 1;
		}else{
			start = middleIndex + 1;
		}
	}

	return firstIndex;
};

console.log(binarySearch([1,2,3,4,4,4,5,6,7,8], 4));