How to use the pegjs/lib/compiler/asts.indexOfRule function in pegjs

parts.push("function peg$parse" + rule.name + "(): " + outputType +" {");

    if (options.trace) {
      parts.push("  const startPos = peg$currPos;");
    }

    for (let i = 0; i <= stack.maxSp; i++) {
      stackVars[i] = s(i);
    }

    parts.push("  let " + stackVars.join(", ") + ";");

    parts.push(indent2(generateRuleHeader(
      "\"" + js.stringEscape(rule.name) + "\"",
      asts.indexOfRule(ast, rule.name)
    )));
    parts.push(indent2(code));
    parts.push(indent2(generateRuleFooter(
      "\"" + js.stringEscape(rule.name) + "\"",
      s(0)
    )));

    parts.push("}");

    return parts.join("\n");
  }

rule_ref(node) {
      return [op.RULE, asts.indexOfRule(ast, node.name)];
    },

          r => r + ": " + asts.indexOfRule(ast, r)
        ).join(", ") +

parts.push([
      "function peg$parse(input: string, options?: IParseOptions) {",
      "  options = options !== undefined ? options : {};",
      "",
      "  const peg$FAILED: Readonly<{}> = {};",
      ""
    ].join("\n"));

    if (options.optimize === "size") {
      let startRuleIndices = "{ " +
        options.allowedStartRules.map(
          r => r + ": " + asts.indexOfRule(ast, r)
        ).join(", ") +
        " }";
      let startRuleIndex = asts.indexOfRule(ast, options.allowedStartRules[0]);

      parts.push([
        "  const peg$startRuleIndices: {[id: string]: number}  = " + startRuleIndices + ";",
        "  let peg$startRuleIndex = " + startRuleIndex + ";"
      ].join("\n"));
    } else {
      let startRuleFunctions = "{ " +
        options.allowedStartRules.map(
          r => r + ": peg$parse" + r
        ).join(", ") +
        " }";
      let startRuleFunction = "peg$parse" + options.allowedStartRules[0];

      parts.push([
        "  const peg$startRuleFunctions: {[id: string]: any} = " + startRuleFunctions + ";",
        "  let peg$startRuleFunction: () => any = " + startRuleFunction + ";"