small javascript engines

Salvatore Sanfilippo asked on twitter for recommendations for small javascript engines to embed in a program, and got a few:

duktape

Duktape

Duktape is an embeddable Javascript engine, with a focus on portability and compact footprint.

Duktape is easy to integrate into a C/C++ project: add duktape.c, duktape.h, and duk_config.h to your build, and use the Duktape API to call ECMAScript functions from C code and vice versa.

quickjs

by Fabrice Bellard

QuickJS is a small and embeddable Javascript engine. It supports the ES2020 specification including modules, asynchronous generators, proxies and BigInt.

It optionally supports mathematical extensions such as big decimal floating point numbers (BigDecimal), big binary floating point numbers (BigFloat) and operator overloading.

Main Features:

• Small and easily embeddable: just a few C files, no external dependency, 210 KiB of x86 code for a simple hello world program.
• Fast interpreter with very low startup time: runs the 75000 tests of the ECMAScript Test Suite in about 100 seconds on a single core of a desktop PC. The complete life cycle of a runtime instance completes in less than 300 microseconds.
• Almost complete ES2020 support including modules, asynchronous generators and full Annex B support (legacy web compatibility).
• Passes nearly 100% of the ECMAScript Test Suite tests when selecting the ES2020 features. A summary is available at Test262 Report.
• Can compile Javascript sources to executables with no external dependency.
• Garbage collection using reference counting (to reduce memory usage and have deterministic behavior) with cycle removal.
• Mathematical extensions: BigDecimal, BigFloat, operator overloading, bigint mode, math mode.
• Command line interpreter with contextual colorization implemented in Javascript.
• Small built-in standard library with C library wrappers.

Espruino:

Espruino is a JavaScript interpreter for microcontrollers. It is designed for devices with as little as 128kB Flash and 8kB RAM.