it works consistently

main.mjs

@@ -41,23 +41,17 @@ const grades = [
 function getGrade(mark){
 
 	if (isNaN(Number(mark))) return 'Ab'
+	if (mark > 100 || mark < 0) return 'OUT OF MARK RANGE'
 
-	for (let i=0;i<=grades.length-1;i++){
-		const {max} = grades[i]
-		printdebug({i,max})
-
-		if (max > mark) continue
-
-		for (let j=i;j>0;j--) {
-			const {min,grade} = grades[j]
-		printdebug({j,min})
-			if (mark < min) continue
-			return grade
+	main: for (let i=0;i<grades.length;i++){
+		printdebug({i})
+		if (mark > grades[i].max) continue
+		while (grades[i].min > mark){
+			if (++i === grades.length) break main
+			printdebug({i})
 		}
+		return grades[i].grade
 	}
-	return 'Ab'
-	//const [{grade}] = grades.filter(({max,min}) => mark <= max && mark >= min)
-	//return grade
 }