Node.js util.inspect must return a string

As explained here:

http://nodejs.org/api/util.html#util_util_inspect_object_options

util.inspect return a string

node/node.d.ts

@@ -1011,7 +1011,7 @@ declare module "util" {
     export function puts(...param: any[]): void;
     export function print(...param: any[]): void;
     export function log(string: string): void;
-    export function inspect(object: any, showHidden?: boolean, depth?: number, color?: boolean): void;
+    export function inspect(object: any, showHidden?: boolean, depth?: number, color?: boolean): string;
     export function isArray(object: any): boolean;
     export function isRegExp(object: any): boolean;
     export function isDate(object: any): boolean;