JavaScript grammar by Positive Technologies

This JavaScript grammar does not exactly corresponds to ECMAScript standard. The main goal during developing was practical usage, performance and clarity (getting rid of duplicates).

Universal Actions & Semantic Predicates

Some modern JavaScript syntax can not be handled with standard context-free grammars, for example detection of get keyword in getters and get identifiers in other cases. Moreover, some parser options can be defined externally (use strict) and should be considered during parsing process.

For such complex syntax actions and predicates are used. This is a first grammar in repository with attempt to use an universal actions and predicates. It works at least for C# and Java runtimes.

Consider the getter rule in grammar:

getter
    : Identifier{p("get")}? propertyName
    ;

Instruction p("get") stands for get the previous token value and return a boolean value as a result of comparison to "get" string.

For Java runtime it described by the following code in Java/JavaScriptBaseLexer.java

protected boolean prev(String str) {
    return _input.LT(-1).getText().equals(str);
}

For C# runtime by Sam Harwell it described by CSharpSharwell/JavaScriptBaseParser.cs

protected bool prev(string str)
{
    return _input.Lt(-1).Text.Equals(str);
}

Furthermore the superClass option should be defined lexer and parser grammar files by the following manner:

options {
    tokenVocab=JavaScriptLexer;
    superClass=JavaScriptBaseParser;
}

Runtimes super class names (JavaScriptLexer, JavaScriptParser) should be the same for correct parser generation.

Syntax support

ECMAScript 6

Grammar supports the following list of ECMAScript 6 features taken from http://es6-features.org:

• Arrow Functions
• Classes
• Constants
• Destructuring Assignment
• Enhanced Object Properties
• Enhanced Regular Expression
• Extended Literals
• Extended Parameter Handling
• Generators
• Internationalization & Localization
• Iterators (not supported for now)
• Map/Set& WeakMap/WeakSet
• Meta-Programming
• Modules (partial support)
• New Build-In Methods
• Promises
• Scoping
• Strict Functions
• Strict Global
• Symbol Type
• Template Literals
• Typed Arrays

See examples directory with test data files.

Outdated

Also this grammar supports outdated syntax such as

• Html Comment
• CData section

Main contributors

• Bart Kiers (2014) - initial version
• Ivan Kochurkin (2017):
  • Updated for EcmaScript 6 support
  • Cleared & optimized
  • Universal code actions & predicates
  • Support of some outdated syntax (Html comment, CData)

License

MIT