ExecJS

ExecJS lets you run JavaScript code from Ruby. It automatically picks the best runtime available to evaluate your JavaScript program, then returns the result to you as a Ruby object.

ExecJS supports these runtimes:

• therubyrhino - Mozilla Rhino embedded within JRuby
• Duktape.rb - Duktape JavaScript interpreter
• Node.js
• Bun.sh - JavaScript runtime & toolkit designed for speed
• Apple JavaScriptCore - Included with Mac OS X
• Microsoft Windows Script Host (JScript)
• Google V8
• mini_racer - Google V8 embedded within Ruby
• GraalVM JavaScript - used on TruffleRuby

A short example:

require "execjs"
ExecJS.eval "'red yellow blue'.split(' ')"
# => ["red", "yellow", "blue"]

A longer example, demonstrating how to invoke the CoffeeScript compiler:

require "execjs"
require "net/http"
source = Net::HTTP.get(URI("https://coffeescript.org/browser-compiler-legacy/coffeescript.js"))

context = ExecJS.compile(source)
context.call("CoffeeScript.compile", "square = (x) -> x * x", bare: true)
# => "var square;\nsquare = function(x) {\n  return x * x;\n};"

Forcing a specific runtime

If you'd like to use a specific runtime rather than the autodetected one, you can assign ExecJS.runtime:

ExecJS.runtime = ExecJS::Runtimes::Node

Alternatively, you can define it via the EXECJS_RUNTIME environment variable:

EXECJS_RUNTIME=Node ruby ...

You can find the list of possible runtimes in lib/execjs/runtimes.rb.

Installation

$ gem install execjs

FAQ

Why can't I use CommonJS require() inside ExecJS?

ExecJS provides the lowest common denominator interface to any JavaScript runtime. Use ExecJS when it doesn't matter which JavaScript interpreter your code runs in. If you want to access the Node API, you should check another library like commonjs.rb designed to provide a consistent interface.

Why can't I use setTimeout?

For similar reasons as modules, not all runtimes guarantee a full JavaScript event loop. So setTimeout, setInterval and other timers are not defined.

Why can't I use ES5 features?

Some runtimes like Node will implement many of the latest ES5 features. However older stock runtimes like JSC on OSX and JScript on Windows may not. You should only count on ES3 features being available. Prefer feature checking these APIs rather than hard coding support for specific runtimes.

Can ExecJS be used to sandbox scripts?

No, ExecJS shouldn't be used for any security related sandboxing. Since runtimes are automatically detected, each runtime has different sandboxing properties. You shouldn't use ExecJS.eval on any inputs you wouldn't feel comfortable Ruby eval()ing.

Contributing to ExecJS

ExecJS is the work of dozens of contributors. You're encouraged to submit pull requests, propose features and discuss issues.

See CONTRIBUTING.

License

ExecJS is released under the MIT License.