JavaScript bookmark that can be used to open interactive R shell in shiny app

r-shell.js

javascript:(function($) {
  var handlers = [];
  if (typeof Shiny !== 'undefined') {
    Shiny.addCustomMessageHandler("__EVAL__", function(data) {
      handlers.forEach(function(handler) {
        handler(data);
      });
    });
  }
  var index = 0;
  function exec(str, callback) {
    if (!str.trim()) {
      return Promise.resolve();
    }
    return new Promise(function(resolve, reject) {
      var id = index++;
      
      handlers.push(function handler(data) {
        if (data.id === id) {
          if (data.error) {
            reject(data.error);
          } else {
            resolve(data.result);
          }
        }
        handlers = handlers.filter(function(f) {
          return f !== handler;
        });
      });
      Shiny.onInputChange('__EVAL__', {id: id, value: str});
    });
  }
  function init() {
    var t = $('div.terminal');
    if (t.length) {
      t.each(function() {
        $(this).terminal().destroy().remove();
      });
    }
    $('.shell-wrapper').remove();
    var wrapper = $('<div>').addClass('shell-wrapper').appendTo('body');
    var nav = $('<nav/>').appendTo(wrapper);
    $('<span class="shell-destroy">[x]</span>').click(function() {
      term.destroy();
      wrapper.remove();
    }).appendTo(nav);

    $.terminal.defaults.formatters = [$.terminal.nested_formatting];
    $.terminal.syntax('r');
    
    var term = window.term = $('<div>').appendTo('body').terminal(function(cmd, term) {
      if (!cmd.trim()) {
        return;
      }
      return exec(cmd).then(function(result) {
        if (result) {
          if (result instanceof Array) {
             result = result.join('\n');
          }
          if (typeof result !== 'string') {
            result = String(result);
          }
          result = result.trim();
          if (result) {
            term.echo($.terminal.escape_brackets(result));
          }
        }
      }).catch(function(e) {
        if (e instanceof Array) {
          e = e.join('\n');
        }
        term.error(e);
      });
    }, {
      greetings: 'R console\n'
    });
    term.appendTo(wrapper);
    $('style.terminal').remove();
    $('<style class="terminal">.terminal { font-size-adjust: none; --size: 1.2;height: calc(100% - 31px); } .shell-wrapper nav {color:#ccc;border-bottom:1px solid #ccc;font-family:monospace;text-align: right;background: black;} .shell-wrapper {position: fixed;z-index:99999;bottom:0;left:0;right:0;height:150px; }.shell-destroy {padding: 5px;cursor:pointer;display: inline-block;}</style>').appendTo('head');
  }
  ['https://unpkg.com/jquery.terminal/css/jquery.terminal.min.css',
   'https://unpkg.com/prismjs/themes/prism-coy.css'
  ].forEach(function(url) {
    var link = $('<link href="' + url + '" rel="stylesheet"/>');
    var head = $('head');
    if (head.length) {
      link.appendTo(head);
    } else {
      link.appendTo('body');
    }
  });
 if ($.terminal && $.terminal.prism) {
  init();
 } else {
  var scripts = [
      'https://unpkg.com/jquery.terminal/js/jquery.terminal.min.js',
      'https://unpkg.com/prismjs/prism.js',
      'https://unpkg.com/jquery.terminal/js/prism.js',
      'https://unpkg.com/prismjs/components/prism-r.min.js'
  ];
  (function recur() {
    var script = scripts.shift();
    if (!script) {
      init();
    } else {
      $.getScript(script, recur);
    }
  })();
 }
})(jQuery);

server.R

#' To use Debugger you need to call debugger.init(input, session)
#' inside shiny server function. Then you need complementary JS code
#' that is avaiable as bookmarklet. Then in any context you call
#' debugger function to change the context (it's optional).
#' If you call that function in constructor you will be able
#' to access self and private properties of the object.

#' eval to string function that work the same as R REPL
#' @param code - string to evaluate
#' @param env - enviroment in which to evaluate the code
#' @export
r.eval <- function(code, env = parent.frame()) {
  paste(
    capture.output(eval(parse(text = code), envir = env)),
    collapse = "\n"
  )
}

#' debugger environment
.global <- list2env(list(env = NULL))

#' function to use instead of browser() and put context of debugger in this place
#' @export
debugger <- function() {
   .global$env <- parent.frame()
}

#' Initialization of the debugger
#' @param session - shiny session
#' @export
debugger.init <- function(session, env = parent.frame()) {
  .global$env <- env
  shiny::observeEvent(session$input[["__EVAL__"]], {
    data <- session$input[["__EVAL__"]]
    tryCatch({
      payload <- list(
        id = data$id,
        result = r.eval(data$value, env = .global$env)
      )
      session$sendCustomMessage("__EVAL__", payload)
    }, error = function(cond) {
      error <- paste(
        capture.output(traceback(cond)),
        collapse = "\n"
      )
      payload <-  list(id = data$id, error = error)
      session$sendCustomMessage("__EVAL__", payload)
    })
  })
}