How to use the antlr4.atn function in antlr4

function parse(input) {
    const chars = new antlr4.InputStream(input);
    const lexer = new ElectroGrammarLexer(chars);
    const tokens = new antlr4.CommonTokenStream(lexer);
    const parser = new ElectroGrammarParser(tokens);

    // enable grammar ambiguity diagnostic output
    // see Antlr book ch 9.2, page 156
    // https://github.com/antlr/antlr4/issues/2206
    parser.removeErrorListeners();
    parser.addErrorListener(new antlr4.error.DiagnosticErrorListener());
    parser._interp.PredictionMode =
      antlr4.atn.PredictionMode.LL_EXACT_AMBIG_DETECTION;

    parser.buildParseTrees = true;

    const tree = parser[start_rule]();
    const listener = new ElectroGrammarToObjectListener();
    const walker = antlr4.tree.ParseTreeWalker.DEFAULT.walk(listener, tree);
    return listener.obj;
  }
  return parse;

"01\u0007(\u0002\u000212\u0007(\u0002\u00022\n\u0003\u0002\u0002\u0002",
    "34\u0007~\u0002\u000245\u0007~\u0002\u00025\f\u0003\u0002\u0002\u0002",
    "67\u0007@\u0002\u00027\u000e\u0003\u0002\u0002\u000289\u0007>\u0002",
    "\u00029\u0010\u0003\u0002\u0002\u0002:;\u0007?\u0002\u0002;<\u0007?",
    "\u0002\u0002<\u0012\u0003\u0002\u0002\u0002=>\u0007@\u0002\u0002>?\u0007",
    "?\u0002\u0002?\u0014\u0003\u0002\u0002\u0002@A\u0007>\u0002\u0002AB",
    "\u0007?\u0002\u0002B\u0016\u0003\u0002\u0002\u0002CE\t\u0005\u0002\u0002",
    "DC\u0003\u0002\u0002\u0002EH\u0003\u0002\u0002\u0002FD\u0003\u0002\u0002",
    "\u0002FG\u0003\u0002\u0002\u0002GI\u0003\u0002\u0002\u0002HF\u0003\u0002",
    "\u0002\u0002IM\t\u0006\u0002\u0002JL\t\u0007\u0002\u0002KJ\u0003\u0002",
    "\u0002\u0002LO\u0003\u0002\u0002\u0002MK\u0003\u0002\u0002\u0002MN\u0003",
    "\u0002\u0002\u0002N\u0018\u0003\u0002\u0002\u0002OM\u0003\u0002\u0002",
    "\u0002\b\u0002\u001c+.FM\u0003\b\u0002\u0002"].join("");


const atn = new antlr4.atn.ATNDeserializer().deserialize(serializedATN);

const decisionsToDFA = atn.decisionToState.map( (ds, index) => new antlr4.dfa.DFA(ds, index) );

export default class PolicyLexer extends antlr4.Lexer {

    static grammarFileName = "Policy.g4";
    static channelNames = [ "DEFAULT_TOKEN_CHANNEL", "HIDDEN" ];
	static modeNames = [ "DEFAULT_MODE" ];
	static literalNames = [ null, null, "'count'", null, "'&&'", "'||'", "'>'", 
                         "'<'", "'=='", "'>='", "'<='" ];
	static symbolicNames = [ null, "WS", "COUNT", "INTLIT", "AND", "OR", "GREATER_THAN", 
                          "LESS_THAN", "EQUAL", "GREATER_THAN_EQUAL", "LESS_THAN_EQUAL", 
                          "ID" ];
	static ruleNames = [ "WS", "COUNT", "INTLIT", "AND", "OR", "GREATER_THAN", 
                      "LESS_THAN", "EQUAL", "GREATER_THAN_EQUAL", "LESS_THAN_EQUAL", 
                      "ID" ];

case PolicyParser.COUNT:
	        case PolicyParser.INTLIT:
	            localctx = new CountExpressionContext(this, localctx);
	            this._ctx = localctx;
	            _prevctx = localctx;
	            this.state = 11;
	            this.count_expression();
	            break;
	        default:
	            throw new antlr4.error.NoViableAltException(this);
	        }
	        this._ctx.stop = this._input.LT(-1);
	        this.state = 22;
	        this._errHandler.sync(this);
	        let _alt = this._interp.adaptivePredict(this._input,2,this._ctx)
	        while(_alt!=2 && _alt!=antlr4.atn.ATN.INVALID_ALT_NUMBER) {
	            if(_alt===1) {
	                if(this._parseListeners!==null) {
	                    this.triggerExitRuleEvent();
	                }
	                _prevctx = localctx;
	                this.state = 20;
	                this._errHandler.sync(this);
	                var la_ = this._interp.adaptivePredict(this._input,1,this._ctx);
	                switch(la_) {
	                case 1:
	                    localctx = new BooleanAndExpressionContext(this, new ExpressionContext(this, _parentctx, _parentState));
	                    this.pushNewRecursionContext(localctx, _startState, PolicyParser.RULE_expression);
	                    this.state = 14;
	                    if (!( this.precpred(this._ctx, 4))) {
	                        throw new antlr4.error.FailedPredicateException(this, "this.precpred(this._ctx, 4)");
	                    }

"\u0004\u0002\u000e\u000b\u0003\u0002\u0002\u0002\u000e\r\u0003\u0002",
    "\u0002\u0002\u000f\u0018\u0003\u0002\u0002\u0002\u0010\u0011\f\u0006",
    "\u0002\u0002\u0011\u0012\u0007\u0006\u0002\u0002\u0012\u0017\u0005\u0004",
    "\u0003\u0007\u0013\u0014\f\u0005\u0002\u0002\u0014\u0015\u0007\u0007",
    "\u0002\u0002\u0015\u0017\u0005\u0004\u0003\u0006\u0016\u0010\u0003\u0002",
    "\u0002\u0002\u0016\u0013\u0003\u0002\u0002\u0002\u0017\u001a\u0003\u0002",
    "\u0002\u0002\u0018\u0016\u0003\u0002\u0002\u0002\u0018\u0019\u0003\u0002",
    "\u0002\u0002\u0019\u0005\u0003\u0002\u0002\u0002\u001a\u0018\u0003\u0002",
    "\u0002\u0002\u001b\u001c\u0007\u0004\u0002\u0002\u001c\u001d\t\u0002",
    "\u0002\u0002\u001d\"\u0007\u0005\u0002\u0002\u001e\u001f\u0007\u0005",
    "\u0002\u0002\u001f \t\u0002\u0002\u0002 \"\u0007\u0004\u0002\u0002!",
    "\u001b\u0003\u0002\u0002\u0002!\u001e\u0003\u0002\u0002\u0002\"\u0007",
    "\u0003\u0002\u0002\u0002\u0006\u000e\u0016\u0018!"].join("");


const atn = new antlr4.atn.ATNDeserializer().deserialize(serializedATN);

const decisionsToDFA = atn.decisionToState.map( (ds, index) => new antlr4.dfa.DFA(ds, index) );

const sharedContextCache = new antlr4.PredictionContextCache();

export default class PolicyParser extends antlr4.Parser {

    static grammarFileName = "Policy.g4";
    static literalNames = [ null, null, "'count'", null, "'&&'", "'||'", 
                            "'>'", "'<'", "'=='", "'>='", "'<='" ];
    static symbolicNames = [ null, "WS", "COUNT", "INTLIT", "AND", "OR", 
                             "GREATER_THAN", "LESS_THAN", "EQUAL", "GREATER_THAN_EQUAL", 
                             "LESS_THAN_EQUAL", "ID" ];
    static ruleNames = [ "root", "expression", "count_expression" ];

    constructor(input) {

constructor(input) {
        super(input);
        this._interp = new antlr4.atn.ParserATNSimulator(this, atn, decisionsToDFA, sharedContextCache);
        this.ruleNames = PolicyParser.ruleNames;
        this.literalNames = PolicyParser.literalNames;
        this.symbolicNames = PolicyParser.symbolicNames;
    }