Tinymce html5 placeholder by reading attribute from textarea

I refactored Tom Duke's code to work on TinyMCE4 with it's jquery plugin

$('textarea.tinymce').tinymce({
  script_url: _base + '/assets/js/tinymce/tinymce.min.js',
  theme: "modern",
  setup: function(editor) {
    // Set placeholder
    var placeholder = $('#' + editor.id).attr('placeholder');
    if (typeof placeholder !== 'undefined' && placeholder !== false) {
      var is_default = false;
      editor.on('init', function() {
        // get the current content
        var cont = editor.getContent();

        // If its empty and we have a placeholder set the value
        if (cont.length === 0) {
          editor.setContent(placeholder);
          // Get updated content
          cont = placeholder;
        }
        // convert to plain text and compare strings
        is_default = (cont == placeholder);

        // nothing to do
        if (!is_default) {
          return;
        }
      })
      .on('focus', function() {
        // replace the default content on focus if the same as original placeholder
        if (is_default) {
          editor.setContent('');
        }
      })
      .on('blur', function() {
        if (editor.getContent().length === 0) {
          editor.setContent(placeholder);
        }
      });
    }
  }
});

I was getting an error if there was no placeholder attribute.

I combined the code from this answer: jQuery hasAttr checking to see if there is an attribute on an element to get the amended code below which deals with that scenario:

setup: function(ed) {

// Set placeholder
var tinymce_placeholder = $('#'+ed.id);
var attr = tinymce_placeholder.attr('placeholder');

// For some browsers, `attr` is undefined; for others,
// `attr` is false.  Check for both.
    if (typeof attr !== 'undefined' && attr !== false) {
        var is_default = false;

        ed.onInit.add(function(ed) {
            // get the current content
            var cont = ed.getContent();

            // If its empty and we have a placeholder set the value
            if(cont.length == 0){
                ed.setContent(tinymce_placeholder.attr("placeholder"));

                // Get updated content
                cont = tinymce_placeholder.attr("placeholder");
            }

            // convert to plain text and compare strings
            is_default = (cont == tinymce_placeholder.attr("placeholder"));

            // nothing to do
            if (!is_default){
                return;
            }
        });

        ed.onMouseDown.add(function(ed,e) {
            // replace the default content on focus if the same as original placeholder
            if (is_default){
                ed.setContent('');
            }
        });
    }
}

The answers above were not working for me, but here's my (for me) working code based on the answers above and using onchange_callback. Hope it helps someone!

onchange_callback : function(ed){
            var tinymce_placeholder = $('#' + ed.id).attr("placeholder");     
            setTimeout(function () {
                var content = ed.getContent().replace(/<p>|<\/p>/g, '');
                if (content == '') {
                    ed.setContent(tinymce_placeholder);
                }
            }, 200);
        },
        setup: function (ed) {
            // Set placeholder
            var tinymce_placeholder = $('#' + ed.id);
            if (tinymce_placeholder.length) {
                ed.onInit.add(function (ed) {
                    var cont = ed.getContent();
                    if (cont.length == 0) {
                        ed.setContent(tinymce_placeholder.attr("placeholder"));
                    }
                });
                ed.onMouseDown.add(function (ed, e) {
                    var content = ed.getContent().replace(/<p>|<\/p>/g, '');
                    if (content == tinymce_placeholder.attr("placeholder")) {
                        ed.setContent('');
                    }
                });
            }
        }