Formatting source with CodeMirror

cmReformat.js

// Editor initialization
var area = $('textarea.text-editor'); // or whatever yours is called

editor = CodeMirror.fromTextArea(area.get(0), {
  mode: {name: "xml", htmlMode: true}, // enables syntax highlighting, need to download the relevant modules
  lineNumbers: true,
  lineWrapping: true,
  tabSize: 2
});

// Re-indent everything
// https://codemirror.net/doc/manual.html#event_change
editor.on("change", reindent(instance));

var reindent = function(cm) {
  var lines = cm.lineCount();
  for (var i = 0; i < lines; i++) {
    cm.indentLine(i);
  };
}