Brainf*ck Interpreter for LINE Messaging API (using Google Apps Script)

Code.js

var ACCESS_TOKEN = '';
var url = 'https://api.line.me/v2/bot/message/reply';

function doPost(e) {
    replyMessage(e);
    return ContentService.createTextOutput(
      JSON.stringify({ content: 'post ok' })
    ).setMimeType(ContentService.MimeType.JSON);
};

var replyMessage = function (e) {
    var userMessage = JSON.parse(e.postData.contents)
      .events[0].message.text;
    var replyToken = JSON.parse(e.postData.contents)
      .events[0].replyToken;

    UrlFetchApp.fetch(url, {
        headers: {
            'Content-Type': 'application/json; charset=UTF-8',
            Authorization: 'Bearer ' + ACCESS_TOKEN
        },
        method: 'post',
        payload: JSON.stringify({
            replyToken: replyToken,
            messages: [
                {
                    type: 'text',
                    text: brain(userMessage)
                }
            ]
        })
    });
};

function brain(text) {
  var code = text
    .replace(/！|\!/g, '>')
    .replace(/？|\?/g, '<')
    .replace(/〜/g, '+')
    .replace(/ー/g, '-')
    .replace(/。/g, '.')
    .replace(/、/g, ',')
    .replace(/（/g, '[')
    .replace(/）/g, ']')
    .replace(/[^><\+-\.,\[\]]/g, "");

  var input = (text + '""')
    .replace(/「|」/g, "\"")
    .match(/".*?"/g)[0]
    .replace(/"/g, "");

  return brainfuck(code, input);
}

function brainfuck(code, input) {
  var ptr = 0;  // pointer
  var mmr = [0, null];  // memory
  var pc = 0; // program counter
  var ic = 0; // input counter
  var tmp = 0;  // to avoid double brackets

  var steps = 0;
  var step_limit = 1000000;

  var output = "";

  for (pc = 0; pc < code.length; pc++) {
    switch (code[pc]) {
      case '>':
        ptr++;
        if (!mmr[ptr]) { // add a space in mmr
          mmr[ptr] = 0;
          mmr.push(null);
        }
        break;
      case '<': ptr--; break;
      case '+': mmr[ptr]++; break;
      case '-': mmr[ptr]--; break;
      case '.':
        output += String.fromCharCode(mmr[ptr]);
        break;
      case ',':
        mmr[ptr] = input.charCodeAt(ic);
        ic++;
        break;
      case '[':
        if (!mmr[ptr]) {
          tmp = 1;
          while (tmp) {
            pc++;
            if (code[pc] == '[') tmp++;
            if (code[pc] == ']') tmp--;
          }
        }
        break;
      case ']':
        if (mmr[ptr]) {
          tmp = 1;
          while (tmp) {
            pc--;
            if (code[pc] == ']') tmp++;
            if (code[pc] == '[') tmp--;
          }
          pc--;
        }
        break;
    }
    steps++;
    if (steps >= step_limit) {
      output = "ERR: There are too many steps.";
      break;
    }
  }
  return output ? output : "ERR: There is no result.";
}