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This page contains notes about using Rust.

See Rust Host for a Rust Accessor Host.

Getting Started

Duktape and Rust

The idea would be to use Rust to interface to Duktape

  • One negative is that Duktape is unsafe, so we would be losing a bunch of safety issues from Duktape
  • One positive is that this could possibly work sooner rather than later
  • We could port eduk to Rust and then start working on a porting Duktape to Rust.

Duktape Rust Interfaces.

JavaScript and Rust

We need a JavaScript interpreter written in Rust.


  • - "Servo is a modern, high-performance browser engine designed for both application and embedded use."... "Sponsored by Mozilla and written in the new systems programming language Rust, the Servo project aims to achieve better parallelism, security, modularity, and performance. "

One idea would be to use the JavaScript interpreter that is presumably part of Servo. It looks like this is possible, though the resulting binary is 19.6Mb in size. Note that the example is merely invoking SpiderMonkey, which is written in C/C++. See below for detail for how to evaluate JavaScript from Rust.

  • "JavaScript and DOM bindings: We are currently using SpiderMonkey, although pluggable engines is a long-term, low-priority goal. Each content task gets its own JavaScript runtime. DOM bindings use the native JavaScript engine API instead of XPCOM. Automatic generation of bindings from WebIDL is a priority."
  • Mac build instructions:
    sudo port install py-virtualenv
    git clone
    cd servo
    # "To build Servo in development mode. This is useful for development, but the resulting binary is very slow."
    ./mach build --dev
    ./mach run tests/html/about-mozilla.html
    # "For benchmarking, performance testing, or real-world use, add the --release flag to create an optimized build:"
    ./mach build --release
    ./mach run --release tests/html/about-mozilla.html


Instead of using all of Servo, we can use rust-mozj, which uses fewer dependencies.

This uses Mozilla SpiderMonkey, but it seems like it is not necessary to install SpiderMonkey separately.

Building rust-mozjs

rust-mozjs uses #[feature]], which requires the nightly build, so as yourself, not as root, install rustup

curl -sSf | sh
source ~/.cargo/env
rustup default nightly

  1. Download
    git clone
  2. Build:
    cd rust-mozjs
    cargo build
  3. target/debug/libjs.rlib is created
  • How can I load an execute some JS code in spider monkey?
    • Suggests, which does not exist
    • However, a copy may be found at
    • merged in on July 2, 2015 describes how the code was added
    • The suggested build command was
      cargo run --features debugmozjs --example callback
    • Build instructions:
          rustup default nightly
          git clone
          cd rust-mozjs
          mkdir examples

          wget -O examples/
          cargo run --example callback  
    • Building failed:
      error[E0432]: unresolved import `js::JSCLASS_RESERVED_SLOTS_SHIFT`                        
        --> examples/                                                          
      12 | use js::{JSCLASS_RESERVED_SLOTS_MASK,JSCLASS_RESERVED_SLOTS_SHIFT,JSCLASS_GLOBAL_SLOT_COUNT,JSCLASS_IS_GLOBAL};                                                                
         |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no `JSCLASS_RESERVED_SLOTS_SHIFT` in `js`. Did you mean to use `JSCLASS_RESERVED_SLOTS_MASK`?  
      • Fix:
        < use js::{JSCLASS_RESERVED_SLOTS_MASK,JSCLASS_RESERVED_SLOTS_SHIFT,JSCLASS_GLOBAL_SLOT_COUNT,JSCLASS_IS_GLOBAL};                                                                    
        > use js::jsapi::{JSCLASS_RESERVED_SLOTS_SHIFT};  
    • Building failed:
      rror[E0560]: struct `js::jsapi::JSClass` has no field named `addProperty`                
        --> examples/                                                            
      25 |     addProperty: None,                                                                
         |     ^^^^^^^^^^^^ field does not exist - did you mean `cOps`?        
      • Solution! Ben Zhang suggested copying tests/ to examples/ and then changing the callback to main. It is also necessary to remove #[test]. The diff is below:
        bash-3.2$ diff tests/ examples/                                      
        < #[test]                                                                                  
        < fn callback() {                                                                          
        > fn main() {                                                                              
    • With the above change, we can compile and run
      bash-3.2$ cargo run --example callback                                                    
         Compiling js v0.1.3 (file:///Users/cxh/src/rust/rust-mozjs)                            
          Finished debug [unoptimized + debuginfo] target(s) in 10.77 secs                      
           Running `target/debug/examples/callback`                                              
      Test Itrntinliztin &#9516;&#9472;&#9516;&#12494;( _ &#12494;)                                                  
    • The binary that is created is 24.5Mb, which can be stripped to 19.6Mb and links to a few system libraries:
      bash-3.2$ ls -l ./target/debug/examples/callback                                          
      -rwxr-xr-x  1 cxh  staff  24529272 Oct 30 16:38 ./target/debug/examples/callback          
      bash-3.2$ strip !$                                                                        
      strip ./target/debug/examples/callback                                                    
      bash-3.2$ ls -l ./target/debug/examples/callback                                          
      -rwxr-xr-x  1 cxh  staff  19561328 Oct 30 16:39 ./target/debug/examples/callback
      bash-3.2$ otool -L ./target/debug/examples/callback                                        
              /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 120.1.0)    
              /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.5)        
              /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1\
    • rust-mozjs seems to have these dependencies:
      bash-3.2$ ls -l target/debug/deps/                                                        
      total 660608                                                                              
      -rw-r--r--  1 cxh  staff     193566 Oct 30 14:17 libbuild-493a7b0628804707.rlib            
      -rw-r--r--  1 cxh  staff     792298 Oct 30 14:17 libcmake-830f3a153d2e04e4.rlib            
      -rw-r--r--  1 cxh  staff    1332660 Oct 30 14:17 libgcc-41d62055fc225d58.rlib              
      -rw-r--r--  1 cxh  staff      47978 Oct 30 14:17 libheapsize-c3a4dd1c77b5ddc8.rlib        
      -rw-r--r--  2 cxh  staff    3488460 Oct 30 16:38 libjs.rlib                                
      -rw-r--r--  1 cxh  staff       6686 Oct 30 14:17 libkernel32-df86a08647459244.rlib        
      -rw-r--r--  1 cxh  staff       9558 Oct 30 14:17 liblazy_static-359f5533c970cd71.rlib      
      -rw-r--r--  1 cxh  staff     438742 Oct 30 14:17 liblibc-ad32fde1bd850538.rlib            
      -rw-r--r--  1 cxh  staff      18694 Oct 30 14:17 liblibz_sys-3ed6726e0477f97a.rlib        
      -rw-r--r--  1 cxh  staff     252172 Oct 30 14:17 liblog-bf16bb9a4912b11d.rlib              
      -rw-r--r--  1 cxh  staff  330085660 Oct 30 14:19 libmozjs_sys-572528194a83d174.rlib        
      -rw-r--r--  1 cxh  staff     670792 Oct 30 14:17 libnum_traits-92bb90166cd1857c.rlib      
      -rw-r--r--  1 cxh  staff     771040 Oct 30 14:17 libpkg_config-7cc12d9787dada57.rlib      
      -rw-r--r--  1 cxh  staff      92406 Oct 30 14:17 libwinapi-0889532d327ff4e2.rlib          

Using rust-mozjs


To use rust-mozjs, you may need to install SpiderMonkey, see

The fastest way seems to be:

  git clone --depth 1
  cd gecko-dev/js/src
  cargo build

JavaScript Rust dead ends

Don't try these:

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Page last modified on November 09, 2016, at 05:23 AM