diff --git a/js/prototype.js b/js/prototype.js
index dd69ae0ebe01bc566af3597fd904200f26470e47..d14c281ce8965d2ffb8048caaa9cfe0b6c5e8de9 100644
--- a/js/prototype.js
+++ b/js/prototype.js
@@ -1,3 +1,9 @@
-String.prototype.capitalize = function() {
-	return this.charAt(0).toUpperCase() + this.substr(1);
+/**
+ * Checks if the number is between two given values.
+ * @param {number} min The minimum value.
+ * @param {number} max The maximum value.
+ * @param {boolean} inclusive Whether or not to include the minimum and maximum values.
+ */
+Number.prototype.between = function(min, max, inclusive = false) {
+	return inclusive ? this >= min && this <= max : this > min && this < max;
 };