add providerType() getter to AbstractProvider

src.ts/providers/abstract-provider.ts

@@ -428,6 +428,8 @@ type CcipArgs = {
     errorArgs: Array<any>
 };
 
+type ProviderType = "jsonrpc" | "etherscan" | "fallback" | "";
+
 /**
  *  An **AbstractProvider** provides a base class for other sub-classes to
  *  implement the [[Provider]] API by normalizing input arguments and
@@ -504,6 +506,17 @@ export class AbstractProvider implements Provider {
      */
     get provider(): this { return this; }
 
+    /**
+     *  Returns a string that identifies the AbstractProvider subclass, for
+     *  better duck typing.
+     */
+    get providerType(): ProviderType {
+        assert(false, "not implemented yet", "NOT_IMPLEMENTED", {
+            operation: "providerType"
+        });
+        return "";
+    }
+
     /**
      *  Returns all the registered plug-ins.
      */

src.ts/providers/provider-etherscan.ts

@@ -142,6 +142,10 @@ export class EtherscanProvider extends AbstractProvider {
         this.getBaseUrl();
     }
 
+    get providerType() {
+        return 'etherscan' as const;
+    }
+
     /**
      *  Returns the base URL.
      *

src.ts/providers/provider-fallback.ts

@@ -414,6 +414,10 @@ export class FallbackProvider extends AbstractProvider {
             "quorum exceed provider wieght", "quorum", this.quorum);
     }
 
+    get providerType() {
+        return 'fallback' as const;
+    }
+
     get providerConfigs(): Array<FallbackProviderState> {
         return this.#configs.map((c) => {
             const result: any = Object.assign({ }, c);

src.ts/providers/provider-jsonrpc.ts

@@ -572,6 +572,10 @@ export abstract class JsonRpcApiProvider extends AbstractProvider {
         }
     }
 
+    get providerType() {
+        return 'jsonrpc' as const;
+    }
+
     /**
      *  Returns the value associated with the option %%key%%.
      *