简单的折半查找

function find2(arr, needle){
	var len = arr.length,
	s=0,e = len -1, m = parseInt(e/2);
	while(s!=e){
		if(arr[m]>needle){
			e = m;
		}
		if(arr[m]<needle){
			s = m;
		}
		if(arr[m]==needle){
			return m;
		}
		m = parseInt((s+e)/2);
	}
}

var mm = [1,2,3,4,5,6,7,8,9,10];

alert(find2(mm, 3));

alert(find2(mm, 4));