Rhino (JavaScript engine)

Rhino
Original author(s)	Norris Boyd
Developer(s)	1997: Mozilla Foundation, 1998: Mozilla Corporation, now developed by volunteers.
Stable release	1.7.14 / January 6, 2022; 2 years ago
Cross-platform
Platform	Java virtual machine
Type	JavaScript engine
License	MPL 2.0
Website	mozilla.github.io/rhino/

Rhino is a

Mozilla Firefox

.

History

The Rhino project was started at

Netscape in 1997. At the time, Netscape was planning to produce a version of Netscape Navigator written fully in Java and so it needed an implementation of JavaScript written in Java. When Netscape stopped work on Javagator, as it was called, the Rhino project was finished as a JavaScript engine. Since then, a couple of major companies (including Sun Microsystems

) have licensed Rhino for use in their products and paid Netscape to do so, allowing work to continue on it.

Originally, Rhino compiled all JavaScript code to Java bytecode in generated Java class files. This produced the best performance, often beating the C++ implementation of JavaScript run with just-in-time compilation (JIT), but suffered from two faults. First, compiling time was long since generating bytecode and loading the generated classes was a resource-intensive process. Also, the implementation effectively leaked memory since most Java virtual machines (JVM) didn't collect unused classes or the strings that are interned as a result of loading a class file.^{[citation needed]} (This has changed in later versions of Java.)

As a result, in the fall of 1998, Rhino added an interpretive mode. The classfile generation code was moved to an optional, dynamically loaded package. Compiling is faster and when scripts are no longer in use they can be collected like any other Java object.

Rhino was released to Mozilla Foundation in April 1998. Originally Rhino classfile generation had been held back from release. However the licensors of Rhino have now agreed to release all of Rhino as open source, including class file generation. Since its release to open source, Rhino has found a variety of uses and an increasing number of people have contributed to the code.^[1] The project gets its name from the animal on the cover of the JavaScript book from O'Reilly Media.^[2] As of version 1.7R11 (May 2019), Rhino supports Java 8 and up, and supports a number of ECMAScript ES6/ES2015 features.^[3]