+.modulus

Author: Dmitry Ovsyanko

lib/Check.js

@@ -6,6 +6,8 @@ module.exports = class {
 		this.checkSumLength = checkSumLength
 		this.totalLength    = totalLength
 
+		this.modulus = 10; for (let i = 1; i < checkSumLength; i ++) this.modulus *= 10
+
 	}
 
 	raise (s, o) {
@@ -54,11 +56,9 @@ module.exports = class {
 
 		this.process (str)
 
-		const {sum} = this; delete this.sum
-
-		return String (this.checkSumLength === 1 ? sum % 11 % 10 : sum % 101 % 100)
+		const {sum, modulus} = this; delete this.sum
 
-			.padStart (this.checkSumLength, '0')
+		return String (sum % (modulus + 1) % modulus).padStart (this.checkSumLength, '0')
 
 	}