Blob feature detection with jQuery (see https://github.com/twbs/bootstrap/pull/12773)

check.js

+function() {
  /**
   * Based on:
   *   Blob Feature Check v1.0.0
   *   https://github.com/ssorallen/blob-feature-check/
   *   License: Public domain (http://unlicense.org)
   */
  var url = window.webkitURL || window.URL // Safari 6 uses "webkitURL".
  var svg = new Blob(
    ['<svg xmlns="http://www.w3.org/2000/svg"></svg>'],
    { type: 'image/svg+xml;charset=utf-8' }
  )
  
  $('<img>')
    .on('error', function() {
      $('.bs-docs-section, .bs-docs-sidebar').css('display', 'none')
      showCallout('Looks like your current browser doesn\'t support the Bootstrap Customizer. Please take a second ' +
                   'to <a href="https://www.google.com/intl/en/chrome/browser/">upgrade to a more modern browser</a>.', true)
    })
    .on('load', function() {
      $compileBtn.prop('disabled', false)
    })
    .attr('src', url.createObjectURL(svg))
}()