Jexl custom evaluator shim

jexl-spike.js

import {elements as defaultGrammar} from 'jexl/lib/grammar.js';
import defaultParser from 'jexl/lib/parser/Parser.js';
import defaultEvaluator from 'jexl/lib/evaluator/Evaluator.js';
import defaultLexer from 'jexl/lib/Lexer.js';
 
export function customEval(
  expr,
  context={},
  {
    transforms={},
    grammar=defaultGrammar,
    parser=defaultParser,
    evaluator=defaultEvaluator,
    lexer=defaultLexer,
  }={}
) {
  const parserInst = new parser(grammar);
  const evaluatorInst = new evaluator(grammar, transforms, context);
  const lexerInst = new lexer(grammar);

  const tokens = lexerInst.tokenize(expr);
  parserInst.addTokens(tokens);
  const ast = parserInst.complete();
  console.log('ast =', JSON.stringify(ast, null, 2));
  return evaluatorInst.eval(ast);
};