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createTarget

Create a data sink. 
createTarget(config: TargetConfig): Target
Parameters:
  • write: Write function async ({ctx, read}) => void (required)
  • fork: Fork handler async (previousBlocks: BlockCursor[]) => BlockCursor | null (optional)
Example: 
const target = createTarget({
  write: async ({ logger, read }) => {
    for await (const { data, ctx } of read()) {
      const span = ctx.profiler.start('save');
      await database.save(data);
      span.end();
    }
  },
});
You can avoid implementing rollback handlers by configuring your source to use only finalized blocks.

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Context & Utilities

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Logger

The logger interface is Pino-compatible. Use ctx.logger in write handlers.

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Profiler

Track performance metrics for pipeline operations. 
interface Profiler {
  start(name: string): Profiler;
  measure<T>(name: string, fn: (span: Profiler) => Promise<T>): Promise<T>;
  addLabels(labels: string | string[]): Profiler;
  end(): Profiler;
  elapsed: number;
  children: Profiler[];
}

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BlockCursor

Cursor format for resuming indexing from a specific block. 
interface BlockCursor {
  number: number;
  hash?: string;
  timestamp?: number;
}
Example: 
const target = createTarget({
  write: async ({ read }) => {
    // Resume from block 20000000
    for await (const { data } of read({ number: 20000000 })) {
      await processData(data);
    }
  }
})