@techmely/utils/mergeStreams.js

Collection of helpful JavaScript / TypeScript utils

'use strict';

var stream = require('stream');

// src/invariant.ts
var prefix = "Invariant failed";
function invariant(condition, message) {
  if (condition) {
    return;
  }
  if (typeof message === "string" || typeof message === "function") {
    const provided = typeof message === "function" ? message() : message;
    const value = provided ? `${prefix}: ${provided}` : prefix;
    throw new Error(value);
  }
  if (message)
    throw message;
  throw new Error(prefix);
}

// src/isArray.ts
function isArray(val) {
  return val && Array.isArray(val);
}

// src/mergeStreams.ts
function mergeStreams(streams) {
  invariant(isArray(streams), "Expect input an array streams");
  const passThroughStream = new stream.PassThrough({ objectMode: true });
  if (streams.length === 0) {
    passThroughStream.end();
    return passThroughStream;
  }
  let streamsCount = streams.length;
  for (const stream of streams) {
    invariant(!(typeof stream?.pipe === "function"), "Expect a stream, got ");
    stream.pipe(passThroughStream, { end: false });
    stream.on("end", () => {
      streamsCount--;
      if (streamsCount === 0) {
        passThroughStream.end();
      }
    });
    stream.on("error", (error) => {
      passThroughStream.emit("error", error);
    });
  }
  return passThroughStream;
}

exports.mergeStreams = mergeStreams;