todo.g4

grammar todo;

elements
    : (element|emptyLine)* EOF
    ;

element
    : '*' ( ' ' | '\t' )* CONTENT NL+
    ;

emptyLine
    : NL
    ;

NL
    : '\r' | '\n' 
    ;

CONTENT
    : [a-zA-Z0-9_][a-zA-Z0-9_ \t]*
    ;

todo.tsx

import { CharStreams, CommonTokenStream } from 'antlr4ts';
import { todoLexer } from './todoLexer';
import { todoListener } from './todoListener';
import { ElementContext, todoParser } from './todoParser';
import { ParseTreeWalker } from 'antlr4ts/tree/ParseTreeWalker'

// Create the lexer and parser
let inputStream = CharStreams.fromString("* hello\n* there\n\n\n")
let lexer = new todoLexer(inputStream);
let tokenStream = new CommonTokenStream(lexer);
let parser = new todoParser(tokenStream);

// Parse the input, where `compilationUnit` is whatever entry point you defined
let tree = parser.elements();

class EnterFunctionListener implements todoListener {
  // Assuming a parser rule with name: `functionDeclaration`
  enterElement(context: ElementContext) {
    console.log(`${context.CONTENT()}`)
  }

  // other enterX functions...
}

// // Create the listener
const listener: todoListener = new EnterFunctionListener();
// // Use the entry point for listeners
ParseTreeWalker.DEFAULT.walk(listener, tree)

// OUTPUT:
// hello
// there