Effects API

Please refer to the documentation website for a thorough guide on all Envio indexer features

With HyperIndex, the Effects API allows you to perform external calls from your handlers. These calls run in parallel with your handler logic, so they don’t block execution.

You can learn more about the Effects API in the documentation: https://docs.envio.dev/docs/HyperIndex/effect-api

The following example extends the factory pattern example to fetch the decimal of a token using an RPC call via Viem.

Create Effect

To create an effect in your handler, use the experimental_createEffect function from the envio package. This function takes two arguments: effect options and a handler function.

Effect options:

• name: used for debugging and logging
• input: the input type of the effect
• output: the output type of the effect
• cache: whether to cache the effect result in the database

Using Effect

To use the effect, use context.effect from your handlers, loaders, or other effects:

CONTRACT.EVENT.handler(async ({ event, context }) => {
  const effectOutput = await context.effect(YOUR_EFFECT, EFFECT_INPUTS);
});

getTokenDetails Effect

The following effect fetches the decimal of a token using an RPC call:

const client = createPublicClient({
  chain: mainnet,
  transport: http(process.env.ETHEREUM_MAINNET_RPC!),
});

const ERC20_ABI = parseAbi(["function decimals() view returns (uint8)"]);

const fetchTokenDetails = experimental_createEffect(
  {
    name: "fetchTokenDetails",
    input: {
      token: S.string,
    },
    output: {
      decimal: S.number,
    },
  },
  async ({ input }) => {
    const decimals = await client.readContract({
      address: input.token as `0x${string}`,
      abi: ERC20_ABI,
      functionName: "decimals",
    });

    console.log(`Token decimals: ${decimals}`);
    return { decimal: decimals };
  }
);

Prerequisites

Before running the indexer locally, make sure you have the following installed:

• Node.js 18+
• pnpm
• Docker Desktop

Running the Indexer

Add your Envio API key to the .env file, then start the indexer:

pnpm dev

If you make changes to config.yaml or schema.graphql, regenerate the type files:

pnpm codegen

GraphQL Playground

While indexer running, visit the Envio Console(https://envio.dev/console) to open the GraphQL Playground and query your indexed data.