Options

Running JavaScript on GraalVM can be configured with several options.

GraalVM JavaScript Launcher Options

These options are to control the behaviour of the js launcher:

• -e, --eval CODE : evaluate the JavaScript source code, then exit the engine.

  js -e 'print(1+2);'
  

• -f, --file FILE: load and execute the provided script file. Note that the -f flag is optional and can be omitted in most cases, as any additional argument to js will be interpreted as file anyway.

  js -f myfile.js
  

• --version: print the version information of GraalVM JavaScript, then exit.
• --strict: execute the engine in JavaScript’s strict mode.

GraalVM JavaScript Engine Options

These options are to configure the behavior of the GraalVM JavaScript engine. Depending on how the engine is started, the options can be passed either to the launcher or programmatically.

Note that most of these options are experimental and require an --experimental-options flag.

To the Launcher

To the launcher, the options are passed with --js.<option-name>=<value>:

js --js.ecmascript-version=6

The following options are currently available:

• --js.annex-b: enable ECMAScript Annex B web compatibility features. Boolean value, default is true.
• --js.array-sort-inherited: define whether Array.protoype.sort should sort inherited keys (implementation-defined behavior). Boolean value, default is true.
• --js.atomics: enable ES2017 Atomics. Boolean value, default is true.
• --js.ecmascript-version: emulate a specific ECMAScript version. Integer value (5-9), default is the latest version.
• --js.foreign-object-prototype: provide JavaScript’s default prototype to foreign objects that mimic JavaScript’s own types (foreign Arrays, Objects and Functions). Boolean value, default is false.
• --js.intl-402: enable ECMAScript Internationalization API. Boolean value, default is false.
• --js.regexp-static-result: provide static RegExp properties containing the results of the last successful match, e.g., RegExp.$1 (legacy). Boolean value, default is true.
• --js.shared-array-buffer: enable ES2017 SharedArrayBuffer. Boolean value, default is false.
• --js.strict: enable strict mode for all scripts. Boolean value, default is false.
• --js.timezone: set the local time zone. String value, default is the system default.
• --js.v8-compat: provide better compatibility with Google’s V8 engine. Boolean value, default is false.

Programmatically

When started from Java via GraalVM’s Polyglot feature, the options are passed programmatically to the Context object:

Context context = Context.newBuilder("js")
                         .option("js.ecmascript-version", "6")
                         .build();
context.eval("js", "42");

See the Polyglot Programming reference for information on how to set options programmatically.

Stable and Experimental Options

The available options are distinguished in stable and experimental options. If an experimental option is used, an extra flag has to be provided upfront.

In the native launchers (js and node), --experimental-options has to be passed before all experimental options. When using a Context, the option allowExperimentalOptions(true) has to be called on the Context.Builder. See ScriptEngine Implementation on how to use experimental options with a ScriptEngine.

ECMAScript Version

This option provides compatibility to a specific version of the ECMAScript specification. It expects an integer value, where both the counting version numbers (5 to 11) and the publication years (starting from 2015) are supported. The default in the development version of GraalVM is the current draft of the specification, currently the ECMAScript 2021 draft specification. Thus, starting with GraalVM 21.0.0, the default will move to the draft ECMAScript 2021 specification. GraalVM JavaScript implements some features of the future draft specification and of open proposals, if you explicitly select that version and/or enable specific experimental flags. For production settings, it is recommended to set the ecmascript-version to an existing, finalized version of the specification.

Available versions are:

• 5 for ECMAScript 5.x
• 6 or 2015 for ECMAScript 2015
• 7 or 2016 for ECMAScript 2016
• 8 or 2017 for ECMAScript 2017
• 9 or 2018 for ECMAScript 2018
• 10 or 2019 for ECMAScript 2019
• 11 or 2020 for ECMAScript 2020 (latest finalized version of the specification)
• 12 or 2021 for ECMAScript 2021 (default, currently in draft stage)
• 13 or 2022 for ECMAScript 2022 (future changes and proposals)

intl-402

This option enables ECMAScript’s Internationalization API. It expects a Boolean value and the default is false.

Strict Mode

This option enables JavaScript’s strict mode for all scripts. It expects a Boolean value and the default is false.