Rhino (JavaScript engine)

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2024-09-05 12:00:04

Rhino is a JavaScript engine written fully in Java and managed by the Mozilla Foundation as open source software. It is separate from the SpiderMonkey engine, which is also developed by Mozilla, but written in C++ and used in Mozilla Firefox.

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.