js-lake-indexer

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NEAR Lake indexer basic tutorial

:::info Source code for the tutorial

near-examples/near-lake-raw-printer-js: source code for the tutorial on how to create an indexer that prints block height and number of shards

::

Recently we have published a JavaScript version of the NEAR Lake Framework on npmjs.org

We want to empower you with a basic tutorial on how to use the JavaScript Library. Let’s get started!

Requirements

Before we get started, please, ensure you have:

Create a project

Create an indexer project:

mkdir near-lake-raw-printer-js && cd near-lake-raw-printer-js

Now we’re going to call npm init, we can continue with the default values pressing Enter on every question in the interactive mode:

npm init
version: (1.0.0)
description:
entry point: (index.js)
test command:
git repository:
keywords:
author:
license: (ISC)
About to write to /Users/near/projects/near-lake-raw-printer-js/package.json:

{
  "name": "near-lake-raw-printer-js",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo "Error: no test specified" && exit 1"
  },
  "author": "",
  "license": "ISC"
}

Is this OK? (yes)

package.json is ready. Let’s install near-lake-framework

Install dependencies

Install near-lake-framework

npm install near-lake-framework --save

Install typescript as dev dependency

npm install typescript --save-dev

Setup TypeScript

Now we can create tsconfig.json for TypeScript settings:

touch tsconfig.json

Paste the content to the file:

{
  "compilerOptions": {
    "lib": [
      "ES2015",
      "dom"
    ]
  }
}

Now let’s add the scripts section to the package.json

"scripts": {
  "start": "tsc && node index.js"
}

After that your package.json should look similar to:

{
  "name": "near-lake-raw-printer",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "tsc && node index.js"
  },
  "dependencies": {
    "near-lake-framework": "^1.0.1"
  },
  "devDependencies": {
    "typescript": "^4.6.4"
  }
}

Now let’s create index.ts

touch index.ts

Open index.ts in your favorite editor to start coding.

Import near-lake-framework

In the index.ts file let’s import the necessary dependencies:

import { startStream, types } from 'near-lake-framework';

We’ve imported the main function startStream which will be called to actually run the indexer, and types that hold the LakeConfig type we need to contruct.

Create a config

To get indexer running we need to start it with a config. We need to create an instance of LakeConfig

const lakeConfig: types.LakeConfig = {
    s3BucketName: "near-lake-data-mainnet",
    s3RegionName: "eu-central-1",
    startBlockHeight: 63804051,
};

Create indexer handler

Indexer will be streaming the StreamerMessage instances we need to handle according to our needs.

In near-lake-framework JS library the handler have to be presented as a callback function. This function have to:

  • be asynchronous
  • accept an argument of type StreamerMessage
  • return nothing (void)

Creating the callback:

async function handleStreamerMessage(streamerMessage: types.StreamerMessage): Promise<void> {
    //
}

For this tutorial our requirement is to log the block height and the numer of shards. That’s simple:

async function handleStreamerMessage(streamerMessage: types.StreamerMessage): Promise<void> {
    console.log(`
        Block #${streamerMessage.block.header.height}
        Shards: ${streamerMessage.shards.length}
    `);
}

Starting the stream

And the last thing to write is the call to startStream with the config and pass the callback function.

(async () => {
    await startStream(lakeConfig, handleStreamerMessage);
})();

That’s it. Now we can compile the code and run it

Compile and run

:::danger Credentials

To be able to access the data from NEAR Lake you need to provide credentials. Please, see the Credentials article

::

We’ve added the start command to the scripts, so the compilation and run should as easy as

npm run start

You should see something like the following:

Block #63804051 Shards: 4
Block #63804052 Shards: 4
Block #63804053 Shards: 4
Block #63804054 Shards: 4
Block #63804055 Shards: 4
Block #63804056 Shards: 4
Block #63804057 Shards: 4
Block #63804058 Shards: 4
Block #63804059 Shards: 4
Block #63804060 Shards: 4

You can stop the indexer by pressing CTRL+C

What’s next?

You can play around and change the content of the callback function handleStreamerMessage to handle the data differently.

You can find the source code for this tutorial on the GitHub.

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