Added GradeBoundaries class

lib/GradeBoundaries.js

@@ -0,0 +1,35 @@
+'use strict';
+
+class GradeBoundaries {
+	boundaries;
+
+	constructor(boundaries = {
+		'A*': 90,
+		'A': 80,
+		'B': 70,
+		'C': 60,
+		'D': 50,
+		'E': 40,
+		'F': 0
+	}) {
+		this.boundaries = boundaries;
+	}
+
+	getGrade(score) {
+		const boundaries = Object.values(this.boundaries);
+
+		for (const [ i, number ] of boundaries.entries()) {
+			if (score >= number)
+				return Object.entries(this.boundaries)[i][0];
+		}
+	}
+
+	toString() {
+		return Object.entries(this.boundaries).reduce((res, b) => {
+			return `${res}\n${b[0]}${' '.repeat(2 - b[0].length)}` +
+				`: >= ${b[1]}`;
+		}, '');
+	}
+}
+
+module.exports = GradeBoundaries;