function binarySearch(items, value){

var startIndex = 0,

stopIndex = items.length - 1,

middle = Math.floor((stopIndex + startIndex)/2);

while(items[middle] != value && startIndex < stopIndex){

//adjust search area

if (value < items[middle]){

stopIndex = middle - 1;

} else if (value > items[middle]){

startIndex = middle + 1;

}

//recalculate middle

middle = Math.floor((stopIndex + startIndex)/2);

}

//make sure it's the right value

return (items[middle] != value) ? -1 : middle;

}

var items = ["a","b","c","d","e","f","g","h","i","j"];

console.log(binarySearch(items, "i")); //8

console.log(binarySearch(items, "b")); //1