1 files changed, 20 insertions, 0 deletions
diff --git a/util/string.ts b/util/string.ts
index 327b884..934963e 100644
--- a/util/string.ts
+++ b/util/string.ts
@@ -32,6 +32,17 @@ declare global {
 		 * `mapFn`
 		 */
 		map(mapFn: (char: string) => string): string;
+
+		/**
+		 * @summary return length of the match of searchValue from startIndex (default: 0)
+		 *
+		 * Similar to String.prototype.startsWith, but returns the length of the
+		 * match instead of a boolean true or false.
+		 *
+		 * @param searchString  string to search for
+		 * @param position  index to search from (0 by default = start of string)
+		 */
+		cmpLen(searchString: string, position?: number): number;
 	}
 }
 
@@ -113,3 +124,12 @@ String.prototype.map = function(mapFn) {
 	return out;
 }
 
+String.prototype.cmpLen = function(searchString, position = 0) {
+	let len = 0;
+	for (let i = 0; i < searchString.length; i++) {
+		if (i + position >= this.length) break;
+		if (this[i + position] == searchString[i]) len++;
+	}
+	return len;
+}
+