RunJS JavaScript Engine

1. Introduction

RunJS is a small JavaScript engine written in JavaScript, no external dependency.

It includes a set of classic JavaScript features in reference to the ECMA-262 Language Specification.

Online Demo

2. Usage

main.js provides a run function that accepts JavaScript source code as an argument.

You can import run anywhere and execute it.

3. Specifications

3.1 Language support

• Primitive data types and object
• Arithmetic and logical operations
• Conditional and iteration statements
• Function and scope

3.2 Standard library

// Similar to console.log()
log(...args);

4. Internals

4.1 Lexer

Implemented lexical analysis using regular expressions.

4.2 Parser

Implemented syntax analysis from scratch according to LL algorithm, and construct AST.

4.3 Runtime

Implemented a set of runtime infrastructure:

• LanguageTypes
  • NumberType (represented as Float64Array)
  • StringType (represented as Uint16Array)
  • BooleanType
  • ObjectType
  • UndefinedType
  • NullType
• Realm
  • The log function is registered here
• SpecificationTypes
  • CompletionRecord
  • LexicalEnvironment
  • Reference
• ExecutionContext

4.4 Evaluator

When a new instance of the JavaScript engine is created, Realm will be created, ExecutionContextStack will be initialized, AST will be traversed and interpreted.