diff --git a/libraries/deno-commons-mod.ts b/libraries/deno-commons-mod.ts
index 845bd2d..51feead 100644
--- a/libraries/deno-commons-mod.ts
+++ b/libraries/deno-commons-mod.ts
@@ -1,4 +1,4 @@
-export function compareVersion(ver1: string, ver2: string) {
+export function compareVersion(ver1: string, ver2: string): 0 | 1 | -1 {
     if (ver1 === ver2) return 0;
     const ver1Parts = ver1.split(".");
     const ver2Parts = ver2.split(".");
@@ -17,12 +17,12 @@ export function compareVersion(ver1: string, ver2: string) {
     return 0;
 }
 
-export function isOn(val: string) {
+export function isOn(val: string): boolean {
     const lowerVal = (val == null) ? val : val.toLowerCase();
     return lowerVal === "on" || lowerVal === "yes" || lowerVal === "1" ||
         lowerVal === "true";
 }
 
-export function isEnvOn(envKey: string) {
+export function isEnvOn(envKey: string): string | undefined {
     return Deno.env.get(envKey);
 }