BESEN is an acronym for "Bero's EcmaScript Engine", and it is a complete
ECMAScript Fifth Edition Implemention in Object Pascal, which is compilable
with Delphi >=7 and FreePascal >= 2.5.1 (maybe also 2.4.1).
BESEN is licensed under a OwnLicense+AGPLv3 dual-license.
Features:
Complete implementation of the ECMAScript Fifth Edition standard
Own bytecode-based ECMA262-complaint Regular Expression Engine
Context-Threaded 32-bit x86 and 64-bit x64/AMD64 Just-in-Time Compiler (a ARMv7 EABI JIT for ARM CPUs with VFPv3 instruction set is planned)
Constant folding
Dead code elimination
Abstract-Syntax-Tree based optimizations
Type inference (both exact and speculative)
Polymorphic Inline Cache based on object structure and property key IDs
Perfomance optimized hash maps
Self balanced trees (for example to sort on-the-fly linked list items of hash maps for very fast enumeration of array objects)
Easy native ObjectPascal class integration (properties per RTTI and published methods per by-hand-parsing of the native virtual method table)
Hints
Function code runs faster than global non-function code, because function-local variable accesses will be always identifier index lookups instead of identifier string lookups.
Strict code runs faster than non-strict code, for that reason please use preferably "use strict" where is it possible, because at strict code is the arguments object creation cheaper at funtion calls, for example no setter/getter creation for each function argument in the arguments object.
Scoping and some other things between ECMAScript 3rd Edition and ECMAScript 5th Edition are a bit different, so the execution perfomance of ES3 code in a ES5-complaint engine can be strong faster or even strong slower, depends on the individual situation/code.
No all old ES3 code must be runnable in a ES5-complaint engine, but the most old ES3 code should be runnable, I think.
