This example demonstrates a reusable JavaScript function for joining two datasets, enabling efficient data combination in visualization workflows. It builds an index from a lookup table and then maps rows from a main table through that index, selecting only the desired columns. The code shows a raw implementation of a lookup-table join, similar to SQL-style joins, with a commented usage example that merges brand and article data. The example relies on plain JavaScript arrays and objects, with no external libraries, making it a lightweight utility for preprocessing data before visualization.