Perform a binary search within an array

function binary_Search(items, value){ var firstIndex = 0, lastIndex = items.length - 1, middleIndex = Math.floor((lastIndex + firstIndex)/2); while(items[middleIndex] != value && firstIndex < lastIndex) { if (value < items[middleIndex]) { lastIndex = middleIndex - 1; } else if (value > items[middleIndex]) { firstIndex = middleIndex + 1; } middleIndex = Math.floor((lastIndex + firstIndex)/2); } return (items[middleIndex] != value) ? -1 : middleIndex; } var items = [1, 2, 3, 4, 5, 7, 8, 9]; console.log(binary_Search(items, 1)); console.log(binary_Search(items, 5));