Reload buffer when file changes in Emacs

I’ve started learning typescript and one of the cool feature of compiler is –watch options that recompile the file when it change it’s content. In Emacs if file is changed the buffer still contain old file and if you try to edit that file you’re ask if you really want to ed it that file because it change content.

It found that it would be nice to have reload when file changes, so I wrote this little bit of Emacs Lisp:

(defun reload ()
  "Revert buffer, then restore previous position."
  (let ((pt  (point)))
    (revert-buffer t t)
    (goto-char pt)))

;; two helpers to work with alists

(defun add-to-alist (symbol name value)
  "Add new pair to ALIST"
  (let* ((list (symbol-value symbol))
         (pair (assoc name list)))
    (if pair
        (setcdr pair value)
      (let ((pair (cons name value)))
        (if list
            (setf (symbol-value symbol) (cons pair list))
          (setf (symbol-value symbol) (cons pair nil)))))
    (symbol-value symbol)))

(defun remove-alist (symbol name)
  "Remove pair from ALIST"
  (let* ((list (symbol-value symbol))
         (pair (assoc name list)))
    (if pair
        (let ((ptr list))
          (if (eq (caar ptr) name)
              (setf (symbol-value symbol) '())
            (while ptr
              (if (eq (caadr ptr) name)
                    (setcdr ptr (cddr ptr))
                    (setq ptr nil))
                (setq ptr (cdr ptr))))

(require 'filenotify)

(setq file-watchers '())

(defun watch ()
  "Function watch file changes and reload the file from buffer"
  (let* ((fname (buffer-file-name))
         (pair (assoc fname file-watchers)))
    (if pair
          (file-notify-rm-watch (cdr pair))
          (remove-alist 'file-watchers descritor)))

    (let ((descriptor (file-notify-add-watch fname
                                             (lexical-let ((filename fname))
                                               (lambda (event)
                                                 (with-current-buffer (get-file-buffer filename)
                                                   (if (not (buffer-modified-p))
                                                         (message "update %s" filename)
      (add-to-alist 'file-watchers fname descriptor))))

Then to watch the file You just need to invoke the function using M-x watch. The function will not reload the buffer if you have modifications. In that case you need to invoke reload function using M-x reload.

This will probably don’t work on windows but I’m not sure, here is documentation for file-notify-* functions.




Run shiny R application from Emacs

Right now I use Windows box for development at work and I use Emacs, but I needed to run RStudio to run the shiny application that I was working on. I though it would be nice to run shiny app from Emacs. On windows I was not able to run ansi-term but eshell was working.

Here is a function that run shiny app if the buffer you’re in is directory that contain server.R:

(defun shiny ()
  "run shiny R application in new shell buffer

  if there is displayed buffer that have shell it will use that window"
  (let* ((R (concat "shiny::runApp('" default-directory "')"))
         (name "*shiny*")
         (new-buffer (get-buffer-create name))
          (apply 'make-comint-in-buffer "script" new-buffer "R" nil `("-e" ,R)))
         (window (get-window-with-mode '(comint-mode eshell-mode)))
       (script-proc (get-buffer-process script-proc-buffer)))
    (if window
        (set-window-buffer window new-buffer)
      (switch-to-buffer-other-window new-buffer))
    (set-process-sentinel script-proc 'special-mode-sentinel)))

(defun search-window-buffer (fn)
  "return first window for witch given function return non nil value"
  (let ((buffers (buffer-list))
    (dolist (buffer buffers value)
      (let ((window (get-buffer-window buffer)))
        (if (and window (not value) (funcall fn buffer window))
            (setq value window)))))))

(defun get-window-with-mode (modes)
  "return window with given major modes"
  (search-window-buffer (lambda (buff window)
                        ((let ((mode (with-current-buffer buffer major-mode)))
                          (member mode modes)))))

I’ve needed to use sentinels because If I run simple eshell command it was freezing Emacs and I need to press C-g to cancel the command, it din’t kill R but it was not very good solution.

I’ve also need to update my switch to other major mode buffer, because I was using Eshell that had eshell-mode and my new shiny buffer had comint-mode, I wanted those buffers it to be treated as the same. Above I’ve defined two functions for searching windows because I was using eshell and I wanted to have R from shiny run in the same window. If you’re using ansi-term (on windows it don’t work) you can check it’s major mode and add it to the list of modes in call to get-window-with-mode.

Below is the code for switching to other buffer with same mode (it’s should be common maybe), using C-M-tab and C-tab.

(setq same-mode-alist '((eshell-mode comint-mode) (comint-mode eshell-mode)))

(defun buffer-same-mode (change-buffer-fun)
  "execute function for next buffer with the same major mode
  or mode on the list in same-mode-alist variable"
  (let ((current-mode major-mode)
        (next-mode nil))
    (while (not (or (eq next-mode current-mode)
                    (member next-mode (cdr (assoc current-mode same-mode-alist)))))
      (funcall change-buffer-fun)
      (setq next-mode major-mode))))

(defun previous-buffer-same-mode ()
  "switch to previous buffer with same mode"
  (buffer-same-mode #'previous-buffer))

(defun next-buffer-same-mode ()
  "switch to next buffer with same mode"
  (buffer-same-mode #'next-buffer))

(global-set-key [C-M-tab] 'previous-buffer-same-mode)
(global-set-key [C-tab] 'next-buffer-same-mode)


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Show code coverage from jest framework in emacs

I recently switched from jasmine/istanbul to jest framework for my project jQuery Terminal and I’ve got coverage drop from 80-81% to about 69% with some update of the code and commented out code that I was working on.

So I thought it would be cool to highlight the lines that where covered and not covered by tests and since I use emacs as my editor I thought that I write a function that will do that.

Here it is:

(defun root-git-repo ()
  (replace-regexp-in-string "\n"
                            (shell-command-to-string "git rev-parse --show-toplevel")))

(defun line-pos-at-line (line)
    (goto-line line)

(defun coverage-mark-buffer ()
  (let* ((dir (root-git-repo))
         (json-object-type 'hash-table)
         (json-array-type 'list)
         (json-key-type 'string)
         (json (json-read-file (concat dir "/coverage/coverage-final.json")))
         (filename (buffer-file-name (current-buffer)))
         (coverage (gethash filename json))
         (statments (gethash "statementMap" coverage)))
      (maphash (lambda (key value)
                 (let* ((statment (gethash key statments))
                        (start (gethash "start" statment))
                        (end (gethash "end" statment))
                        (start-line-pos (line-pos-at-line (gethash "line" start)))
                        (start-pos (+ start-line-pos (gethash "column" start)))
                        (end-line-pos (line-pos-at-line (gethash "line" start)))
                        (end-pos (+ end-line-pos (gethash "column" end)))
                        (color (if (= value 0) "dark red" "dark green"))
                        (face `((t (:background ,color)))))
                    (hlt-highlight-region start-pos end-pos face)))
               (gethash "s" coverage)))))

The function is using hlt-highlight-region from highlight.el by Drew Adams.

The function don’t check if coverage file exists. It assume that you’re opening from from git repo and that coverage file is in coverage directory (default for jest) in git root.

The function is quite slow, and it need to process a lot, if the file is big. You can see how it look like in this page, generated by Emacs library htmlize.

If you want to clear the buffer you can use this function:

(defun coverage-clear-buffer ()
    (hlt-unhighlight-region 0 (point))))

Clear is much faster.

If you’re iterested in code coverage in Emacs you can take a look at jest-coverage minor mode that I’ve created based on this solution.

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How to create Web Server from Browser

In my GIT Web Terminal I use BrowserFS to write files (it’s required by isomorphic-git that I use to create git interface in browsers).
BrowserFS is implementation of node fs module but for browsers, it use few types of storage, I use indexedDB same as example for isomorphic-git.

I thought that i would be cool to edit the project itself and be able to view the files when I edit them in the browser (before I commit), like they where serve from web server. And it turn out it’s possible with Service Worker since you can access IndexedDB from that worker and you can create HTTP response from string or from arrayBuffer (BrowserFS is returning arrayBuffer from its readFile function).

Here is the code for service worker that show pages and directory listing:

self.addEventListener('install', function(evt) {
    BrowserFS.configure({ fs: 'IndexedDB', options: {} }, function (err) {
        if (err) {
        } else {
            self.fs = BrowserFS.BFSRequire('fs');
            self.path = BrowserFS.BFSRequire('path');

self.addEventListener('fetch', function (event) {
    event.respondWith(new Promise(function(resolve, reject) {
        function sendFile(path) {
            fs.readFile(path, function(err, buffer) {
                if (err) {
                    err.fn = 'readFile(' + path + ')';
                    return reject(err);
                resolve(new Response(buffer));
        var url = event.request.url;
        var m = url.match(/__browserfs__(.*)/);
        function redirect_dir() {
            return resolve(Response.redirect(url + '/', 301));
        if (m && self.fs) {
            var path = m[1];
            if (path === '') {
                return redirect_dir();
            console.log('serving ' + path + ' from browserfs');
            fs.stat(path, function(err, stat) {
                if (err) {
                    return resolve(textResponse(error404(path)));
                if (stat.isFile()) {
                } else if (stat.isDirectory()) {
                    if (path.substr(-1, 1) !== '/') {
                        return redirect_dir();
                    fs.readdir(path, function(err, list) {
                        if (err) {
                            err.fn = 'readdir(' + path + ')';
                            return reject(err);
                        var len = list.length;
                        if (list.includes('index.html')) {
                            sendFile(path + '/index.html');
                        } else {
                            var output = [
                            if (path.match(/^\/(.*\/)/)) {
                                output.push('<li><a href="..">..</a></li>');
                            (function loop() {
                                var file = list.shift();
                                if (!file) {
                                    output = output.concat(['</ul>', '', '']);
                                    return resolve(textResponse(output.join('\n')));
                                fs.stat(path + '/' + file, function(err, stat) {
                                    if (err) {
                                        err.fn = 'stat(' + path + '/' + file + ')';
                                        return reject(err);
                                    var name = file + (stat.isDirectory() ? '/' : '');
                                    output.push('<li><a href="' + name + '">' + name + '</a></li>');
        } else {
function textResponse(string) {
    var blob = new Blob([string], {
        type: 'text/html'
    return new Response(blob);

function error404(path) {
    var output = [
        '<h1>404 File Not Found</h1>',
        `File ${path} not found in browserfs`,
    return output.join('\n');

Service worker is using __browserfs__ marker to distinguish normal url from urls that are from BrowserFS/IndexedDB. Everything after it it’s serve from BrowserFS. So if you write file foo you can access it using __browserfs__/foo. Here is the code sample that will create a file using browserFS:

fs.writeFile('/foo', 'hello world', function(err) {
   if (err) {
     console.log('Error write file');

You can see how this work in my GIT Web Terminal just clone any repo (best is the one that have directories) and view files with url

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How to create D3 Plugin

I was learning D3 and wanted to write plugin attrs, that will allow to use object to set attributes on svg DOM nodes. It seems that this functionality was in D3 but was removed.

I was searching and was not able to fine how to create the plugins, but then I look at source code for d3 transition (it’s easier to search bundle file than original files on github).

And at the end, there was code that I’ve needed to use. That’s what I thought it require to add to prototype.

So here is my attrs plugin:

d3.selection.prototype.attrs = function(attrs) {
  this.each(function(d, i) {
    var element =;
    Object.keys(attrs).forEach((key) => {
      element.attr(key, attrs[key]);
  return this;

You can use it like normal attr:

var g ='body')
  .attrs({width: 200, height: 200})
    x: 50,
    y: 50,
    width: 100,
    height: 100,
    stroke: 'rgb(255, 100, 100)',
    'stroke-width': 10,
    fill: 'black'

It works the same as jQuery plugins.

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How to add GPS coordinate to your photo using data from google

I have Nikon DSLR and I wanted to add GPS location so when I upload them to flickr I have it on a map and don’t need to add location by hand.

If you have android phone, you don’t need any extra GPS hardware, to have GPS location on your photos taken with your camera.

The solution, if you have GPS enabled in your phone is it take location history from google map using this url: (export option is in dropdown in gear icon at the bottom)

You will have JSON file with GSP coordinates and timestamps for all your locations from your phone.

Now to extract the GPS out of JSON file I use this small script written in Python, it use exiftool to write EXIF back to the file because PIL can only read exif not write it.

#!/usr/bin/env python

from __future__ import division
import simplejson as json
from PIL import Image
from dateutil import parser
from optparse import OptionParser
from subprocess import call
from datetime import datetime, timedelta

def get_date_taken(path):

def nearest(items, pivot):
    return min(items, key=lambda x: abs(x - pivot))

def comparator(date, hours_shift = None):
    def compare(x):
        current = datetime.fromtimestamp(int(x['timestampMs']) / 1000.0)
        if hours_shift is not None:
            current = current + timedelta(seconds = hours_shift * 60 * 60)
        return abs(current - date)
    return compare

def get_gps(gps, date, hours_shift = None):
    return min(gps['locations'], key=comparator(date, hours_shift))

def parse_date(str):
    return datetime.strptime(str, "%Y:%m:%d %H:%M:%S")

def timestamp(dt, epoch=datetime(1970,1,1)):
    td = dt - epoch
    return (td.microseconds + (td.seconds + td.days * 86400) * 10**6) / 10**6

def timezone(date, hours):
    return date - timedelta(seconds = hours * 60 * 60)

if __name__ == '__main__':
    from sys import argv
    opt = OptionParser()
    opt.add_option('-l', '--location')
    opt.add_option('-t', '--timezone')
    (options, args) = opt.parse_args()
    if options.location is None or len(args) != 1:
        print "usage %s [--timezone <hours shift>] --location [History JSON File] <IMAGE FILE>" % argv[0]
        gps_list = json.loads(open(options.location).read())
        date = parse_date(get_date_taken(args[0]))
        if options.timezone is not None:
            loc = get_gps(gps_list, date, int(options.timezone))
            loc = get_gps(gps_list, date)
        found = datetime.fromtimestamp(
            int(loc['timestampMs']) / 1000.0
        print "%s == %s" % (date, found)
            '-GPSLatitude=%s' % str(int(loc['latitudeE7']) / 1e7),
            '-GPSLongitude=%s' % str(int(loc['longitudeE7']) / 1e7),

To use it you need to use terminal and execute --location &lt;PATH TO JSON&gt; &lt;JPEG File&gt;

The only one issue I’ve found is that PIL can’t extract exif from RAW/NEF files, so you can only use JPEG but you can write exif to RAW/NEF but read create time out of JPG file, if you shot in both JPG and RAW like I do.

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How to simulate error for http requests in R application

I was working on shiny R application and the app was using xmlParse(path) to parse url from web API I was using. I needed to add error handling to respond to 404 and 500 errors, so I’ve changed my code to use httr library. That way I could use two steps process of getting xml from API.

My code look like this:

      res <- GET(url)
      if (res$status_code == 500) {
        message <- "Error From API" 
      } else if (res$status_code == 404) {
        message <- paste("Study", .session$sid, "not found")
      } else if (res$status_code != 200) {
        message <- paste(
          "Unknown response code",
          "for Study",
      studyXML <- tryCatch(
          content(res, "text", encoding = "UTF-8"),
        error = function(e) {
           simpleFatalError("parse error")

and now I had the problem how to simulate 500 error because that error in the API that was needed to be handled was fixed by the API team. So what I’ve did was installing Fiddler I work on windows if you work on Linux better would be to use Burp Suite.

And I used Fiddler script which seems simpler solution because it was just one line of code:

    static function OnBeforeResponse(oSession: Session) {
        if (m_Hide304s && oSession.responseCode == 304) {
            oSession["ui-hide"] = "true";
        if (oSession.url.Contains("study.xml")) { // this was part of the url that returned xml from API
            oSession.oRequest.FailSession(500, "Blocked", "Fiddler blocked this file");

But I had the problem that Fiddler was not handling my backed requests. And it turn out that I needed to enable proxy for httr which is as simple as:

res <- GET(path, use_proxy("", 8888))

Then I was able to test my connecting to the API, and get proper error in shiny app.

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