Compiling in browsers

Both the nearley parser and compiled grammars work in browsers; simply include nearley.js and your compiled grammar.js file in <script> tags and use nearley as usual. However, the nearley compiler is not designed for the browser – you should precompile your grammars and only serve the generated JS files to browsers.

If you absolutely have to compile a grammar in a browser (for example, to implement a nearley IDE) then you can use a tool like Webpack or Rollup to include the nearley NPM package in your browser code. Then, you can utilize the nearleyc internals to compile grammars dynamically.

const nearley = require("nearley");
const compile = require("nearley/lib/compile");
const generate = require("nearley/lib/generate");
const nearleyGrammar = require("nearley/lib/nearley-language-bootstrapped");

function compileGrammar(sourceCode) {
    // Parse the grammar source into an AST
    const grammarParser = new nearley.Parser(nearleyGrammar);
    const grammarAst = grammarParser.results[0]; // TODO check for errors

    // Compile the AST into a set of rules
    const grammarInfoObject = compile(grammarAst, {});
    // Generate JavaScript code from the rules
    const grammarJs = generate(grammarInfoObject, "grammar");

    // Pretend this is a CommonJS environment to catch exports from the grammar.
    const module = { exports: {} };

    return module.exports;

const grammar = compileGrammar("main -> foo | bar");

const parser = new nearley.Parser(nearley.Grammar.fromCompiled(grammar));