Internal CodeEngine utilities

Usage no npm install needed!

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CodeEngine utilities

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This is a utility library that's used inside CodeEngine. It contains miscellaneous utility functions, some of which are experimental and may be removed or changed in the future.

NOTE: This is an internal library that is only intended to be used by CodeEngine. Using it outside of CodeEngine is discouraged.

Table of Contents

File utilities

createFile(info, [pluginName])

Creates a CodeEngine File object.

  • info: - A FileInfo object. All fields are optional except for the path.

  • pluginName: - (optional) The name of the plugin that's creating the file. This is used to create a unique source URL for the file. If not provided, it just defaults to "plugin".

import { createFile } from "@code-engine/utils";

createFile({ path: "robots.txt" });
createFile({ path: "page.html", text: "<h1>Hello, world!</h1>" });
createFile({ path: "img/logo.jpg", contents: Buffer.from([0, 1, 0, 1, 1]) });

createChangedFile(info, [pluginName])

This is the same as createFile(), except that it requires a change property to be set (to "created", "modified", or "deleted").

import { createChangedFile } from "@code-engine/utils";

createChangedFile({ path: "robots.txt", change: "created" });
createChangedFile({ path: "page.html", text: "<h1>Hello, world!</h1>", change: "modified" });


Normalizes a FileInfo object. For ease of use, the FileInfo interface is pretty loose and allows multiple different data types for most fields. This function returns a normalized FileInfo object where each field is a specific type.

This function is called internally by createFile() and createChangedFile().

import { normalizeFileInfo } from "@code-engine/utils";

normalizeFileInfo({ path: "robots.txt" });
normalizeFileInfo({ path: "page.html", text: "<h1>Hello, world!</h1>" });

Module utilities

resolveModule(moduleId, [cwd])

Resolves the entry-file path of the specified JavaScript module, either from the specified path or a globally-installed NPM package.

  • moduleId: - The name or path of the module to resolve

  • cwd - (optional) The directory to resolve from. Defaults to process.cwd()

import { resolveModule } from "@code-engine/utils";

resolveModule("lodash", "/my/custom/path");

importModule(moduleId, [cwd])

Imports the specified JavaScript module, either from the specified path or a globally-installed NPM package.

  • moduleId: - The name or path of the module to resolve

  • cwd - (optional) The directory to resolve from. Defaults to process.cwd()

import { importModule } from "@code-engine/utils";

importModule("lodash", "/my/custom/path");

Iteration utilities

ConcurrentTasks class

This class helps when running multiple async tasks concurrently. Given a concurrency limit, it tracks availability to run additional tasks.

import { ConcurrentTasks } from "@code-engine/utils";

// Run up to 3 async tasks concurrently
let concurrentTasks = new ConcurrentTasks(3);

// Process a large list of files, 3 at a time
for await (let file of files) {
  // Wait for one of the 3 task "slots" to become available
  await concurrentTasks.waitForAvailability();

  // Start an async task
  let promise = processFile(file);

// Wait for any remainint tasks to complete
await concurrentTasks.waitForAll();

IterableWriter class

Creates an async iterable that you can write values to.

import { IterableWriter } from "@code-engine/utils";

// The writer.iterable property is the async iterable that gets written to
let writer = new IterableWriter();

// Write a value to the iterable, and wait for it to be read
await writer.write("Some value");

// Cause the iterable to throw an error on the next read
await writer.throw(new Error("Boom!"));

// Indicate that there are no more values, and wait for all existing values to be read.
await writer.end();


Iterates over anything. This can be a single value, an array of values, an iterable, an async iterable, a Promise that returns one or more values. Literally anything.

This function is used to allow CodeEngine plugins to return files however they want. They can return a single file, an array of files, an async iterator of files, a Promise of files, etc. If the plugin returns undefined, then that's the same as returning an empty array (i.e. no files).

import { iterate } from "@code-engine/utils";

// undefined is the same as an empty list
for await (let value of iterate(undefined)) {
  console.log("This line will never be executed");

// Iterate over a single async value
let promise = Promise.resolve({ path: "some-file.txt" });

for await (let file of iterate(promise)) {
  console.log(`Processing file: ${file.path}`);

// Iterate over an array of values
let files = [
  { path: "file1.txt" },
  { path: "file2.txt" },
  { path: "file3.txt" },

for await (let file of iterate(files)) {
  console.log(`Processing file: ${file.path}`);

iterateParallel(iterable, concurrency)

Iterates over an async iterable, always reading the specified number of values at a time. Values are yielded in first-available order.

  • iterable: - An async iterable

  • concurrency: - The number of values to read simultaneously

import { iterateParallel } from "@code-engine/utils";

// Read 3 files at a time from disk. Some files may take longer to read than others.
// The loop iterates each file in first-available order.
for await (let file of iterateParallel(myAsyncFileReader, 3)) {
  console.log(`Processing file: ${file.path}`);


Joins multiple iterables into a single one that yields values in first-available order.

  • iterables: - The iterables (sync and/or async) to join together
import { joinIterables } from "@code-engine/utils";

let source1 = readFilesFrom("/my/first/directory");
let source2 = readFilesFrom("/my/second/directory");
let source3 = readFilesFrom("/my/third/directory");

// Read files from all three sources, and process them in first-available order
for await (let file of joinIterables(source1, source2, source3)) {
  console.log(`Processing file: ${file.path}`);

splitIterable(iterable, concurrency)

Splits an iterable into separate ones that each iterate a subset of the values. Each value in the original iterable will only be sent to ONE of the separate iterables. Values are sent in a first-come, first-serve order, so some iterables may receive more values than others.

  • iterable: - The iterable to split

  • concurrency: - The number of separate iterables to create

import { splitIterable } from "@code-engine/utils";

// Split one async iterable into three
let [iterable1, iterable2, iterable3] = splitIterable(myAsyncIterable, 3);

debounceIterable(iterable, delay)

Debounces an async iterable, so all values that are yielded within a threshold are grouped together.

  • iterable: - An async iterable

  • delay: - The amount of time, in milliseconds, to wait for additional values before yielding

import { debounceIterable } from "@code-engine/utils";

// Each iteration of this loop will wait at least 300ms.
// The values variable contains all values that were yielded since the previous iteration.
for await (let values of debounceIterable(myAsyncIterable, 300)) {
  console.log(`${values.length} values were yielded`);

drainIterable(iterable, [concurrency])

Iterates over all values in an async iterable, optionally multiple values at a time. The values are immediately discarded, so very little memory is consumed.

  • iterable: - An async iterable

  • concurrency: - (optional) The number of values to read simultaneously. Defaults to 1.

import { drainIterable } from "@code-engine/utils";

// Iterate over all values, one at a time
await drainIterable(myAsyncIterable);

// Iterate over all values, three at a time
await drainIterable(myAsyncIterable, 3);

Log utilities

log(logger, level, message, [data])

This is just a convenience function that calls the corresponding method of the Logger object.

  • logger: - A Logger object

  • level: - A severity level, which determines which Logger method to call. Can be "info", "log", "debug", "warn", "warning", or "error".

  • message: - The string or Error object to log

  • data: (optional) A POJO with additional data to log

import { log } from "@code-engine/utils";

log(myLogger, "info", "This is an info message");
log(myLogger, "warning", "This is a warning!", { code: "LOW_MEMORY" });
log(myLogger, "error", new RangeError("Out of range!"));

createLogEmitter(emitter, [debug])

Creates a Logger that emits log messages via the given EventEmitter.

  • emitter: - The EventEmitter to which logs are emitted

  • debug: - (Optional) A boolean that indicates whether debug messages should be emitted

import { createLogEmitter } from "@code-engine/utils";
import { EventEmitter } from "events";

let emitter = new EventEmitter();
let log = createLogEmitter(emitter, true);

log("This is a log message");
log.warn("This is a warning message");


Contributions, enhancements, and bug-fixes are welcome! Open an issue on GitHub and submit a pull request.


To build the project locally on your computer:

  1. Clone this repo
    git clone https://github.com/CodeEngineOrg/code-engine-utils.git

  2. Install dependencies
    npm install

  3. Build the code
    npm run build

  4. Run the tests
    npm test


@code-engine/utils is 100% free and open-source, under the MIT license. Use it however you want.

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