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V8.Extended

Table Of Content

About

V8.Extended is a small package to add useful common utilities to a ClearScript.V8 JavaScript Engine. This include things like console, setTimeout, path, fs, etc.

All host objects imitate nodejs / browsers standard behavior as closely as possible, but not 100% of APIs are implemented.

In addition to the JavaScript-side API, V8.Extended provides a host-side (C#) API to fine-tune and control some of the APIs behavior. For example, you can lock the fs module to a specific folder, or modify console colors.

With V8.Extended enabled, the following code would work:

console.log("Will write file after one second..");
setTimeout(function() {
    fs.writeFileSync(path.join('subdir', 'hello.txt'), 'hello world!');
    console.log("File saved!");
}, 1000);

To see more code examples check out V8.Extended.Demo, or look at the tests code at V8.Extended.Tests.

NuGet

Package NuGet can be found here: https://www.nuget.org/packages/V8.Extended.

Usage

V8.Extended comes with a set of modules you can attach to a running V8 engine to extend its functionality. Each module can be added separately, so you can control which modules to add.

Console

Implements the basic logging methods of the console object, including trace, debug, info, log, warn, error and assert. By default, will output logs to System.Console with different colors per log level.

Add To Engine

To add the console module:

// v8 is a V8ScriptEngine instance.
V8Extended.Console _console = new();
_console.Extend(v8);

Usage Example

v8.Execute("console.debug('hello', 'world!');");

Additional Options

Colors

You can enable / disable console colors:

// enable colors (default to true)
_console.UseColors = true;

And set which color to use per log level:

// set error level logs to red
_console.LogLevelColor[V8Extended.ConsoleLevel.Error] = ConsoleColor.Red;

Custom Handlers

You can add custom handlers to handle console log calls:

// add a custom handler to copy all console output to an object called `myLogger`.
// return true to continue to next handler, or false to break the chain (will also skip the default `System.Console` part).
_console.AddHandler((string msg, V8Extended.ConsoleLevel level) =>
{
    myLogger.Write(msg);
    return true;
});

Intervals

Implements setTimeout, setInterval, clearTimeout and clearInterval, as standard browsers have.

Add To Engine

To add the intervals module:

// v8 is a V8ScriptEngine instance.
V8Extended.Intervals _intervals = new();
_intervals.Extend(v8);

In addition to attaching the JavaScript module to the V8 engine, you also need to update the timers from C# side. You can do it automatically in a background thread:

// start timers in background. call _intervals.StopEventsLoop(); to stop
_intervals.StartEventsLoopBackground();

Or in the same thread:

// start timers in current thread. call _intervals.StopEventsLoop(); to stop
_intervals.StartEventsLoop();

Or call it manually however you like (recommended to call this every 1 ms, so that timers will not suffer from delays):

_intervals.DoEvents();

Usage Example

v8.Execute("setTimeout(function() { console.debug('1000 ms passed!'); }, 1000);");

Additional Options

Pause

Temporarily pause the events loop.

ClearAll()

Clear all timeouts and intervals.

OnException

Optional errors handler you can attach to handle exceptions from inside the timers execution.

WriteExceptionsToConsole

If true (default) and exception occurs from inside a timeout / interval callback, it will automatically use the console object to write error to console before propagating the error.

If console is not set, will skip it.

Path

Implements the nodejs path module.

The following methods / members are implemented:

  • sep
  • delimiter
  • join()
  • normalize()
  • parse()
  • basename()
  • dirname()
  • extname()
  • format()
  • isAbsolute()
  • resolve()

To learn more about these methods, please see nodejs docs on Path module.

Add To Engine

To add the path module:

// v8 is a V8ScriptEngine instance.
V8Extended.Path _path = new();
_path.Extend(v8);

Usage Example

v8.Execute("var filePath = path.join('hello', 'world!');");

Filesystem

Implements the nodejs fs module.

The following methods / members are implemented:

  • readFile()
  • writeFile()
  • appendFile()
  • readdir()
  • exists()
  • unlink()
  • rename()
  • renameFile()
  • renameDir()
  • mkdir()
  • rmdir()
  • stat()

Plus the following non-standard methods:

  • getType() -> returns 'file', 'dir' or 'none'.
  • isdir()
  • isfile()

Note that every fs method have three versions to it:

  • The regular method (eg fs.readFile), which accepts a callback with (err, returnVal) to be called when operation is complete.
  • The Sync version (eg fs.readFileSync), which blocks until completion and return the value directly (will throw exception on errors).
  • The Promise version (located under fsPromises, eg fsPromises.readFile), which returns a promise.

To learn more about these methods, please see nodejs docs on the fs module.

Add To Engine

To add the fs module:

// v8 is a V8ScriptEngine instance.
V8Extended.Filesystem _fs = new();
_fs.Extend(v8);

Usage Example

v8.Execute($"fs.writeFileSync('test.txt', 'hello world!');");

Additional Options

RootFolder

Set the root folder all filesystem-related operation will be relative to.

LockPathRoot()

If called, will permanently lock all operation to be inside the RootFolder folder (ie preventing the script from leaving that folder) and will also block the ability to change the root folder. For example, if the JavaScript part tries to write file at "../filename.txt" an exception will be thrown.

This action is irreversible, unless you create and attach a new filesystem module to the v8 engine.

Note: I tested most basic cases but there's a chance I've missed something, so please use carefully and at your own risk.

TextEncoder / TextDecoder

Implements the TextEncoder and TextDecoder classes, which are currently missing from V8.

The following methods / members are implemented:

  • encode()
  • decode()
  • encoding

Note: does not support the TextDecodeOptions optional argument.

Add To Engine

To add the encoding classes:

// v8 is a V8ScriptEngine instance.
V8Extended.TextEncoder _enc = new();
_enc.Extend(v8);

This will add both TextEncoder and TextDecoder classes.

Usage Example

v8.Execute($"let textBytes = (new TextEncoder()).encode('hello world!');");

Additional Options

decodePart()

Additional method in TextDecoder that accept additional params, start and end, to decode just a part of the buffer.

Changes

1.0.1

  • Added TextEncoder and TextDecoder classes.

1.0.2

  • Fixed filesystem async methods to not throw exception when no callback is provided.
  • Fixed filesystem async and promises to be actually async.
  • Extended the demo project.
  • Updated ClearCode and V8 versions to latest (don't affect package, just for compatibility testing).

1.0.3

  • Fixed bug with timeouts execution.
  • Improved intervals and timeouts code.

1.0.4

  • Fixed running intervals / timers in background thread / loop to work properly + updated tests.

License

V8.Extended is distributed under the permissive MIT license.