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The QuickJS-ng standard library provides essential functionality for file I/O, operating system interactions, and data serialization. It is implemented in quickjs-libc.c and is available as part of the qjs executable.
The standard library is not part of the core QuickJS engine. It is provided separately as a C library that can be integrated into applications.

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Architecture

The standard library consists of three main modules:

qjs:std

Core utilities including file I/O, environment variables, and script evaluation

qjs:os

Operating system functions for process management, signals, timers, and workers

qjs:bjson

Binary JSON serialization using QuickJS internal format

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Module Imports

To use the standard library modules, import them using the qjs: protocol: 
import * as std from 'qjs:std';
import * as os from 'qjs:os';
import * as bjson from 'qjs:bjson';

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Global Helpers

When using the qjs executable, several global functions and variables are automatically available without imports. See Global Functions for details.

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Platform Support

The standard library supports multiple platforms:
  • Linux - Full support for all features
  • macOS - Full support for all features
  • Windows - Full support with some API differences
  • WASI - Limited support (no popen, tmpfile, worker threads)
Some functions like os.Worker, os.mkstemp, and os.mkdtemp are not available on Windows and WASI platforms.

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Error Handling

Most OS-level functions follow consistent error handling patterns:
  • Return 0 on success
  • Return -errno on failure (negative error code)
  • Use std.Error constants to check specific errors
  • Use std.strerror(errno) to get human-readable error messages
import * as std from 'qjs:std';
import * as os from 'qjs:os';

const fd = os.open('file.txt', os.O_RDONLY);
if (fd < 0) {
  const errno = -fd;
  if (errno === std.Error.ENOENT) {
    console.log('File not found');
  } else {
    console.log('Error:', std.strerror(errno));
  }
}

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Thread Safety

The standard library supports multi-threading through os.Worker:
  • Workers run in separate threads with isolated contexts
  • Communication happens via message passing (similar to Web Workers)
  • SharedArrayBuffer can be shared between workers
  • Signal handlers can only be set in the main thread

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Next Steps

Global Functions

Learn about globally available functions in the qjs executable

Standard Module

Explore file I/O and utility functions

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