<script>
// 19:08

var	input = [1,2,3,4,5,6,7,8,9,10,11];
var	input_string = 4;

function bin_search(input_string, input)
{
	if( input.length == 0) return null;
	var a=0;
	var b=input.length;
	while(a!=b)
	{
		c=a+Math.floor((b-a)/2);
		if( input[c] == input_string)
			return c;
		else if( input[c]>input_string )
		{
			console.log('big a=c');
			b = c
		}
		else if( input[c]<input_string )
		{
			console.log('less');
			a = c;
		}

	}
	return null;
}

alert(bin_search(input_string, input) );
</script>