nginx map for outdated or unsupported browser redirect based on browserslist output

browser-rewrite.conf

# include in the server section of the conf.

# ---------------------------------------------------------------
# If we perform a rewrite on every immediately, images won't be 
# displayed, so we have to avoid the rewrite for specific files
# in support of displaying the outdated page.
#
set $browser_unsupported_rewrite     do_not_perform;

if ($outdated){
  set $browser_unsupported_rewrite   perform;
}

# rewrite images used on page to png instead of svg for really outdated browsers
if ($outdated = 2){
  rewrite ^(/error/)(.*).svg$ $1$2.png last;
}

if ($uri ~* \.(jpeg|jpg|png|gif|svg|css)$) {
  set $browser_unsupported_rewrite   do_not_perform;
}

if ($browser_unsupported_rewrite = perform) {
  rewrite  ^  /error/browser-unsupported.html;
  break;
}

browsers-map.conf

# include in the http section of the conf.

# originally from https://serverfault.com/a/617223/327530

# Use browserslist to generate a current list and match the regexes below to match outdated browser ranges.
# @see https://github.com/browserslist/browserslist
# "production": [
#   ">0.2%",
#   "not dead",
#   "not op_mini all",
#   "not ie < 100",
#   "not edge < 19"
# ],
# yarn browserslist


# blacklist specific browser version ranges that are outdated or simply unsupported.
# @see https://developers.whatismybrowser.com/useragents/explore/ for sample user agents
map $http_user_agent $outdated {
  default                                 0;
  # 1 - outdated but supports svg
  # 2 - outdated so much that we need to rewrite svg to png

  # -------------------------------------------
  # Safari
  #
  # Allow:
  # safari 12
  # safari 11.1
  # Mozilla/5.0 (iPad; CPU OS 12_2 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/5.1 Mobile/15E148 Safari/604.1
  "~AppleWebKit.*Version/[0-9]\..*Safari"  2;    
  "~AppleWebKit.*Version/10.*Safari"       2;   
  "~AppleWebKit.*Version/11\.0.*Safari"    1;  

  # -------------------------------------------
  # ie 11
  #
  # Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; .NET4.0C; .NET4.0E; rv:11.0) like Gecko
  # https://github.com/faisalman/ua-parser-js/blob/master/src/ua-parser.js#L264
  "~Trident/.*"                           2;

  # -------------------------------------------
  # ie edge EdgeHTML (abandoned for ie edge Chromium)
  #
  # Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/17.17134    
  "~Edge/.*"                              1;

  # -------------------------------------------
  # ie edge Chromium (allowed)
  # Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.18 Safari/537.36 Edg/75.0.139.4

  # -------------------------------------------
  # Chrome  
  #
  # Allow:
  # chrome 73
  # chrome 72
  # chrome 71
  # chrome 70
  # chrome 69
  # chrome 63
  # chrome 61
  # chrome 49
  # Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.131 Safari/537.36    
  "~Chrome/[0-9]\."                       2;
  "~Chrome/[0-3][0-9]\."                  2;
  "~Chrome/4[0-8]\."                      1;

  # -------------------------------------------
  # Firefox
  #  
  # Allow:
  # firefox 66
  # firefox 65
  # firefox 52    
  # Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:67.0) Gecko/20100101 Firefox/67.0
  "~Mozilla.*Firefox/[1-9]\."             2;
  "~Mozilla.*Firefox/[0-4][0-9]\."        1;
  "~Mozilla.*Firefox/5[0-1]\."            1;

  # -------------------------------------------
  # Opera
  #  
  # Allow:
  # opera 58
  # Opera/9.80 (X11; Linux x86_64; U; fr) Presto/2.9.168 Version/11.50
  "~Opera.*Version/[0-9].*"               2;
  # Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36 OPR/55.0.2994.61
  "~OPR/[0-1]\."                          2;
  "~OPR/[0-1][0-4]\."                     2;
  "~OPR/5[0-7]\."                         1;
}