Execute ECMAScript code uniformly across any ECMAScript host environment. See also eshost-cli for an easy way to use this library from the command line.
Using eshost
, you can create an agent (eg. a web browser or a command-line ECMAScript host) and evaluate scripts within that agent. Code running within the agent has access to the eshost
runtime API which enables code to evaluate scripts, create new realms, handle errors, and so forth all without worrying about the host-specific mechanisms for these capabilities are.
eshost
consists of a wrapper around the various ways of executing a host and processing its output (called an Agent) and a runtime library for host-agnostic scripts to use.
npm install eshost
Host | Name | Type | Supported Platforms | Download | Notes |
---|---|---|---|---|---|
ch¹ | ChakraCore | CLI | Any | Download or build | Chakra console host. |
d8¹ | V8 | CLI | Any | Build from source | V8 console host. Errors are reported on stdout. Use $262.getGlobal and $262.setGlobal to get and set properties of global objects in other realms. |
engine262 | Engine262 | CLI | Any | Build from source | An implementation of ECMA-262 in JavaScript. |
graaljs | GraalJS | CLI | Any | Download | |
jsshell¹ | SpiderMonkey | CLI | Any | Download | SpiderMonkey console host. |
jsc¹ | JavaScriptCore | CLI | Mac² | Build from source³ | |
kiesel | Kiesel | CLI | Any | Download | |
ladybird-js | Ladybird LibJS | CLI | Any | Build from source | |
nashorn | Nashorn | CLI | Any | Build from source | |
njs | NJS | CLI | Any | Build from source | |
node | Node.js | CLI | Any | https://nodejs.org | Active LTS versions only |
qjs4 | QuickJS | CLI | Any | Build from source | |
xs | Moddable XS | CLI | Any | Build from source | |
chrome | Google Chrome | Browser | Any | Requires ChromeDriver in your path. | |
edge | Microsoft Edge | Browser | Windows | Errors reported from Microsoft Edge are all of type Error. Requires Microsoft WebDriver in your path. | |
firefox | Mozilla Firefox | Browser | Any | Requires GeckoDriver in your path (possibly renamed to wires ). |
|
safari | Apple Safari | Browser | Mac | Requires SafariDriver browser extension. |
- 1:
eshost
acceptsesvu
orjsvu
style binary name values as the first argument toeshost.createAgent(type: string, options = {}): Agent
. See Installing Engines. - 2: It is possible to build
jsc
on other platforms, but not supported. - 3: Also available on your Mac system at
/System/Library/Frameworks/JavaScriptCore.framework/Versions/A/Resources/jsc
. - 4: For QuickJS installation help, see Install and Configure Hosts.
esvu or jsvu are the recommended tools for maintaining JavaScript engines for testing purposes. Take a look at the esvu supported engines or jsvu supported engines for more information.
const eshost = require('eshost');
const agent = await eshost.createAgent('d8', { hostPath: 'path/to/d8.exe' });
const result = await agent.evalScript(`
print(1+1);
`);
console.log(result.stdout);
The eshost
object is the main export of the "eshost" module.
An array of supported host types.
Creates an instance of a host agent for a particular host type. See the table above for supported host types.
-
type
Shells:
Host Type All Acceptable type
ValuesChakraCore chakra
,ch
Engine262 engine262
GraalJS graaljs
Hermes hermes
JavaScriptCore javascriptcore
,jsc
Kiesel kiesel
Ladybird LibJS ladybird-js
,libjs
Nashorn nashorn
Node node
QuickJS qjs
1SpiderMonkey jsshell
,spidermonkey
,sm
V8 d8
,v8
XS xs
- 1: DO NOT USE
~/.jsvu/quickjs
WITH ESHOST-CLI. The mainquickjs
binary does not support the eshost runtime API. For more, see Install and Configure Hosts.
Browsers:
Host Type All Acceptable type
Valueschrome chrome
edge edge
firefox firefox
safari safari
- 1: DO NOT USE
-
options
Property Description hostPath
Path to host to execute. For console hosts, this argument is required. For the specific browser runners, hostPath is optional and if omitted, the location for that browser will be detected automatically. hostArguments
Command line arguments used when invoking your host. Not supported for browser hosts. hostArguments
is an array of strings as you might pass to Node's spawn API.transform
A function to map the source to some other source before running the result on the underlying host. webHost
for web browser hosts only; URL host name from which to serve browser assets; optional; defaults to "localhost"
webPort
for web browser hosts only; URL port number from which to serve browser assets; optional; defaults to 1337
capabilities
for remote
host only; the Selenium/WebDriver capabilities to request for the remote session; all specified attributes will be forwarded to the server; a listing of available attributes is available in the Selenium project's wiki; the following attributes are required:{ browserName, platform, version }
webdriverServer
for remote
host only; URL of the WebDriver server to which commands should be issued
Initializes the host and returns a promise that is resolved once the host is initialized. Command line hosts have no initialization as a new process is started for each execution.
This is called for you if you use the createAgent factory.
Executes code
in the host using the Script goal symbol. Returns a promise for a result object.
When evalScript
receives a Test262File
test record, it executes record.contents
in the host using the Script goal symbol, unless record.attrs.flags.module === true
, in which case it will execute record.contents
in the host using the Module goal symbol. Returns a promise for a result object.
By default, a script will run in eshost
until the realm is destroyed. For most command-line hosts, this is done automatically when the script execution queues are empty. However, browsers will remain open waiting for more code to become available. Therefore, eshost
will automatically append $262.destroy()
to the end of your scripts. This behavior is not correct if you are attempting to execute asynchronous code. In such cases, add async: true
to the options.
-
options
Property Description Default Value async
Set to true
if the test is expected to call$262.destroy()
on the root realm when it's finished. When false,$262.destroy()
is added for you.false
An object with the following keys:
Property | Description |
---|---|
stdout |
Anything printed to stdout (mostly what you print using print ). |
stderr |
Anything printed to stderr |
error |
If the script threw an error, it will be an error object. Else, it will be null. |
The error
object is similar to an error object you get in the host itself. Namely, it has the following keys:
Property | Description |
---|---|
name |
Error name (eg. SyntaxError , TypeError , etc.) |
message |
Error message, if available. |
stack |
An array of stack frames, if available. |
Stops the currently executing script. For a console host, this simply kills the child process. For browser hosts, it will kill the current window and create a new one.
Destroys the agent, closing any of its associated resources (eg. browser windows, child processes, etc.).
Tears down the agent. For browsers, this will close the browser window. For most CLI/Shell hosts, this is a no-op.
Prints str
to stdout.
A reference to the global object.
Creates a new realm, returning that realm's runtime library ($).
For example, creating two nested realms:
$sub = $262.createRealm();
$subsub = $sub.createRealm();
You can also use a destroy callback that gets called when the code inside the realm calls $262.destroy()
. For example:
$sub = $262.createRealm({
destroy() {
print('destroyed!')
}
});
$sub.evalScript('$262.destroy()'); // prints "destroyed!"
-
options
Property Description globals
An object containing properties to add to the global object in the new realm. destroy
A callback that is called when the code executing in the realm destroys its realm (ie. by calling $262.destroy()
).
Creates a new script and evals code
in that realm. If an error is thrown, it will be passed to the onError callback.
Scripts are different from eval in that lexical bindings go into the global lexical contour rather than being scoped to the eval.
Destroys the realm. Note that in some hosts, $262.destroy may not actually stop executing code in the realm or even destroy the realm.
Gets a global property name.
Sets a global property name to value.
This project's tests can be executed with the following command:
npm test
The above command will cause tests to be run against all supported hosts.
Executables for each host must be available on the system's PATH
environment
variable.
One or more hosts may be skipped from the test run by setting corresponding
environment variables whose name match the pattern ESHOST_SKIP_*
, where *
is the capitalized name of the host. For example, in a Unix-like system, the
following command executes the project's tests but skips JavaScriptCore and D8
tests:
ESHOST_SKIP_JSC=1 ESHOST_SKIP_D8=1 npm test
Tests for the "remote" agent can be configured to run against any arbitrary
Selenium/WebDriver configuration through the specification of the following
environment variables: ESHOST_REMOTE_BROWSERNAME
, ESHOST_REMOTE_VERSION
,
ESHOST_REMOTE_PLATFORM
. These values are used to define the host's
capabilities; see the above documentation of eshost.createAgent
for more
details. For example, in a Unix-like system, the following command executes the
project's tests in a remote instance of the Firefox web browser:
ESHOST_REMOTE_BROWSERNAME=firefox npm test