isAddress/validateAddress functions (#946)

packages/util-crypto/src/base64/is.ts

@@ -3,7 +3,7 @@
 
 import { base64Validate } from './validate';
 
-export function isBase64 (value?: string | null): boolean {
+export function isBase64 (value?: string | null): value is string {
   try {
     return base64Validate(value);
   } catch (error) {

packages/util-crypto/src/base64/validate.ts

@@ -7,9 +7,9 @@ import { assert } from '@polkadot/util';
  * @name base64Validate
  * @summary Validates a base64 value.
  * @description
- * Validates the the supplied value is valid base64
+ * Validates that the supplied value is valid base64
  */
-export function base64Validate (value?: string | null): true {
+export function base64Validate (value?: string | null): value is string {
   assert(value, 'Expected non-null, non-empty base64 input');
   assert(/^(?:[A-Za-z0-9+/]{2}[A-Za-z0-9+/]{2})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$/.test(value), 'Invalid base64 encoding');