jdk.scripting.nashorn (Java SE 10 & JDK 10 )
Keywords: jdk.scripting.nashorn module

# Module jdk.scripting.nashorn

Provides the implementation of Nashorn script engine and the runtime environment for programs written in ECMAScript 5.1.

Nashorn is a runtime environment for programs written in ECMAScript 5.1.

# Usage

The recommended way to use Nashorn is through the JSR-223 "Scripting for the Java Platform" APIs found in the `javax.script` package. Usually, you'll obtain a `ScriptEngine` instance for Nashorn using:

    import javax.script.*;
    ...
    ScriptEngine nashornEngine = new ScriptEngineManager().getEngineByName("nashorn");

and then use it just as you would any other JSR-223 script engine. See `jdk.nashorn.api.scripting` package for details.

# Compatibility

Nashorn is 100% compliant with the ECMA-262 Standard, Edition 5.1. It requires a Java Virtual Machine that implements the JSR-292 "Supporting Dynamically Typed Languages on the Java Platform" specification (often referred to as "invokedynamic"), as well as the already mentioned JSR-223.

# Interoperability with the Java platform

In addition to being a 100% ECMAScript 5.1 runtime, Nashorn provides features for interoperability of the ECMAScript programs with the Java platform. In general, any Java object put into the script engine's context will be visible from the script. In terms of the standard, such Java objects are not considered "native objects", but rather "host objects", as defined in section 4.3.8. This distinction allows certain semantical differences in handling them compared to native objects. For most purposes, Java objects behave just as native objects do: you can invoke their methods, get and set their properties. In most cases, though, you can't add arbitrary properties to them, nor can you remove existing properties.

## Java collection handling

Native Java arrays and `List`s support indexed access to their elements through the property accessors, and `Map`s support both property and element access through both dot and square-bracket property accessors, with the difference being that dot operator gives precedence to object properties (its fields and properties defined as `getXxx` and `setXxx` methods) while the square bracket operator gives precedence to map elements. Native Java arrays expose the `length` property.

## ECMAScript primitive types

ECMAScript primitive types for number, string, and boolean are represented with `Number`, `CharSequence`, and `Boolean` objects. While the most often used number type is `Double` and the most often used string type is `String`, don't rely on it as various internal optimizations cause other subclasses of `Number` and internal implementations of `CharSequence` to be used.

## Type conversions

When a method on a Java object is invoked, the arguments are converted to the formal parameter types of the Java method using all allowed ECMAScript conversions. This can be surprising, as in general, conversions from string to number will succeed according to Standard's section 9.3 "ToNumber" and so on; string to boolean, number to boolean, Object to number, Object to string all work. Note that if the Java method's declared parameter type is `java.lang.Object`, Nashorn objects are passed without any conversion whatsoever; specifically if the JavaScript value being passed is of primitive string type, you can only rely on it being a `java.lang.CharSequence`, and if the value is a number, you can only rely on it being a `java.lang.Number`. If the Java method declared parameter type is more specific (e.g. `java.lang.String` or `java.lang.Double`), then Nashorn will of course ensure the required type is passed.

## SAM types

As a special extension when invoking Java methods, ECMAScript function objects can be passed in place of an argument whose Java type is so-called "single abstract method" or "SAM" type. While this name usually covers single-method interfaces, Nashorn is a bit more versatile, and it recognizes a type as a SAM type if all its abstract methods are overloads of the same name, and it is either an interface, or it is an abstract class with a no-arg constructor. The type itself must be public, while the constructor and the methods can be either public or protected. If there are multiple abstract overloads of the same name, the single function will serve as the shared implementation for all of them, and additionally it will also override any non-abstract methods of the same name. This is done to be consistent with the fact that ECMAScript does not have the concept of overloaded methods.

## The `Java` object

Nashorn exposes a non-standard global object named `Java` that is the primary API entry point into Java platform-specific functionality. You can use it to create instances of Java classes, convert from Java arrays to native arrays and back, and so on.

## Other non-standard built-in objects

In addition to `Java`, Nashorn also exposes some other non-standard built-in objects: `JSAdapter`, `JavaImporter`, `Packages`

Since:
  9

- - ### Packages

    Exports
    Package | Description
    --- | ---
    jdk.nashorn.api.scripting | This package provides the `javax.script` integration, which is the preferred way to use Nashorn.
    jdk.nashorn.api.tree | Nashorn parser API provides interfaces to represent ECMAScript source code as abstract syntax trees (AST) and Parser to parse ECMAScript source scripts.

    Indirect Exports
    From | Packages
    --- | ---
    java.scripting | javax.script

  - ### Modules

    Requires
    Modifier | Module | Description
    --- | --- | ---
    transitive | java.scripting | Defines the Scripting API.

  - ### Services

    Provides
    Type | Description
    --- | ---
    ScriptEngineFactory |