diff --git a/src/Date.ts b/src/Date.ts
index c045675..f891e24 100644
--- a/src/Date.ts
+++ b/src/Date.ts
@@ -7,18 +7,48 @@ define(Date, {
 });
 
 define(Date.prototype, {
-	setTimezone: function (timezone: string) {
+	setTimezone: function (this: Date, timezone: string) {
 		return new Date(
 			this.toLocaleString("en-US", {
 				timeZone: timezone,
 			})
 		);
 	},
-	isInPast: function () {
+	isInPast: function (this: Date) {
 		const today = new Date();
 		today.setHours(0, 0, 0, 0);
 		return this < today;
 	},
+	addYear: function (this: Date, years: number, month: number = 0, date: number = 0) {
+		return this.setFullYear(this.getFullYear() + years, this.getMonth() + month, this.getDate() + date);
+	},
+	addMonth: function (this: Date, months: number, date: number = 0) {
+		return this.setMonth(this.getMonth() + months, this.getDate() + date);
+	},
+	addDate: function (this: Date, days: number) {
+		return this.setDate(this.getDate() + days);
+	},
+	addHours: function (this: Date, hours: number, minutes: number = 0, seconds: number = 0, milliseconds: number = 0) {
+		return this.setHours(
+			this.getHours() + hours,
+			this.getMinutes() + minutes,
+			this.getSeconds() + seconds,
+			this.getMilliseconds() + milliseconds
+		);
+	},
+	addMinutes: function (this: Date, minutes: number, seconds: number = 0, milliseconds: number = 0) {
+		return this.setMinutes(
+			this.getMinutes() + minutes,
+			this.getSeconds() + seconds,
+			this.getMilliseconds() + milliseconds
+		);
+	},
+	addSeconds: function (this: Date, seconds: number, milliseconds: number = 0) {
+		return this.setSeconds(this.getSeconds() + seconds, this.getMilliseconds() + milliseconds);
+	},
+	addMilliseconds: function (this: Date, milliseconds: number) {
+		return this.setMilliseconds(this.getMilliseconds() + milliseconds);
+	},
 });
 
 declare global {
@@ -27,7 +57,7 @@ declare global {
 		 * Returns the current timestamp as its representation in seconds
 		 * @returns {number} date in seconds
 		 * @example
-		 * Date.nowSeconds() // 1671621321
+		 * Date.nowSeconds()
 		 */
 		nowSeconds(): number;
 	}
@@ -51,6 +81,55 @@ declare global {
 		 * new Date("2022-12-01").isInPast() // returns: true
 		 */
 		isInPast(): boolean;
+		/**
+		 * Add a number of years to the current date
+		 * @returns {number} timestamp in milliseconds
+		 * @example
+		 * new Date().addYear(1)
+		 */
+		addYear(years: number, month?: number, date?: number): number;
+		/**
+		 * Add a number of months to the current date
+		 * @returns {number} timestamp in milliseconds
+		 * @example
+		 * new Date().addMonth(1)
+		 */
+		addMonth(months: number, date?: number): number;
+		/**
+		 * Add a number of days to the current date
+		 * @returns {number} timestamp in milliseconds
+		 * @example
+		 * new Date().addDate(1)
+		 */
+		addDate(days: number): number;
+		/**
+		 * Add a number of hours to the current date
+		 * @returns {number} timestamp in milliseconds
+		 * @example
+		 * new Date().addHours(1)
+		 */
+		addHours(hours: number, minutes?: number, seconds?: number, milliseconds?: number): number;
+		/**
+		 * Add a number of minutes to the current date
+		 * @returns {number} timestamp in milliseconds
+		 * @example
+		 * new Date().addMinutes(1)
+		 */
+		addMinutes(minutes: number, seconds?: number, milliseconds?: number): number;
+		/**
+		 * Add a number of seconds to the current date
+		 * @returns {number} timestamp in milliseconds
+		 * @example
+		 * new Date().addSeconds(1)
+		 */
+		addSeconds(seconds: number, milliseconds?: number): number;
+		/**
+		 * Add a number of milliseconds to the current date
+		 * @returns {number} timestamp in milliseconds
+		 * @example
+		 * new Date().addMilliseconds(1)
+		 */
+		addMilliseconds(milliseconds: number): number;
 	}
 }
 
diff --git a/src/String.ts b/src/String.ts
index c84cc01..4cbaece 100644
--- a/src/String.ts
+++ b/src/String.ts
@@ -14,39 +14,38 @@ define(String.prototype, {
 	replaceAll: function (find: string, replace: string) {
 		return this.replace(new RegExp(escapeRegExp(find), "g"), replace);
 	},
-	similarity: function (second: string) {
-		const first = this.replace(/\s+/g, "");
-		second = second.replace(/\s+/g, "");
-		if (!first.length && !second.length) return 1; // if both are empty strings
-		if (!first.length || !second.length) return 0; // if only one is empty string
-		if (first === second) return 1; // identical
-		if (first.length === 1 && second.length === 1) return 0; // both are 1-letter strings
-		if (first.length < 2 || second.length < 2) return 0; // if either is a 1-letter string
-		const firstBigrams = new Map();
-		const lowBigrams = new Map();
-		for (let i = 0; i < first.length - 1; i++) {
-			const bigram = first.substring(i, i + 2);
-			const count = firstBigrams.has(bigram) ? firstBigrams.get(bigram) + 1 : 1;
-			const countLow = lowBigrams.has(bigram.toLowerCase()) ? lowBigrams.get(bigram.toLowerCase()) + 1 : 1;
+	similarity: function (s2: string) {
+		var s1 = this.toLowerCase();
+		s2 = s2.toLowerCase();
 
-			lowBigrams.set(bigram.toLowerCase(), countLow);
-			firstBigrams.set(bigram, count);
+		if (s1.length < s2.length) {
+			s1 = s2;
+			s2 = this;
 		}
-		let intersectionSize = 0;
-		for (let i = 0; i < second.length - 1; i++) {
-			const bigram = second.substring(i, i + 2);
-			const count = firstBigrams.has(bigram) ? firstBigrams.get(bigram) : 0;
-			const countLow = firstBigrams.has(bigram.toLowerCase()) ? firstBigrams.get(bigram.toLowerCase()) : 0;
-			if (count > 0) {
-				firstBigrams.set(bigram, count - 1);
-				intersectionSize++;
-			}
-			if (countLow > 0) {
-				firstBigrams.set(bigram.toLowerCase(), countLow - 1);
-				intersectionSize += 0.9;
+		var longerLength = s1.length;
+		if (longerLength == 0) {
+			return 1.0;
+		}
+
+		var costs = new Array();
+		for (var i = 0; i <= s1.length; i++) {
+			var lastValue = i;
+			for (var j = 0; j <= s2.length; j++) {
+				if (i == 0) costs[j] = j;
+				else {
+					if (j > 0) {
+						var newValue = costs[j - 1];
+						if (s1.charAt(i - 1) != s2.charAt(j - 1))
+							newValue = Math.min(Math.min(newValue, lastValue), costs[j]) + 1;
+						costs[j - 1] = lastValue;
+						lastValue = newValue;
+					}
+				}
 			}
+			if (i > 0) costs[s2.length] = lastValue;
 		}
-		return (2.0 * intersectionSize) / (first.length + second.length - 2);
+
+		return (longerLength - costs[s2.length]) / parseFloat(longerLength);
 	},
 	join: function (iterate: string[]) {
 		if (typeof iterate === "string") return iterate;