Find String Position

function stringPosition(needle, haystack) {
		              var m = needle.length,
		                  n = haystack.length;

		              if (!m || !n || m > n) {
		                return -1;
		              }

		              if (m === n) {
		                return needle === haystack ? 0 : -1;
		              }

		              for (var j = 0; j < n; j++) {
	                  for (var i = 0; i < m; i++) {
	                    if (needle[i] !== haystack[i + j]) {
	                      break;
	                    }

	                    if (i === m - 1) {
	                      return j;
	                    }
	                  }

		              }

		              return -1;
	            	}