**flatstr** is a tiny Node.js module that forces a heavily‑concatenated JavaScript string to be “flattened” into a contiguous C‑array inside V8, eliminating the internal rope/tree representation. By calling `flatstr(str)` right before the string is handed to non‑V8 code (e.g., `fs.WriteStream`, XHR, or DOM APIs), developers can gain 20‑50 % speed‑ups on I/O‑heavy workloads. It’s aimed at Node (and browser) developers who build high‑throughput applications that perform a lot of string concatenation before writing or transmitting the result.