ionic-framework/js/views/navBarView.js

(function(ionic) {

  ionic.views.NavBar = function(opts) {
    this.el = opts.el;

    this._titleEl = this.el.querySelector('.title');
  };

  ionic.views.NavBar.prototype = {
    shouldGoBack: function() {},

    setTitle: function(title) {
      if(!this._titleEl) {
        return;
      }
      this._titleEl.innerHTML = title;
    },

    showBackButton: function(shouldShow) {
      var _this = this;

      if(!this._currentBackButton) {
        var back = document.createElement('a');
        back.className = 'button back';
        back.innerHTML = 'Back';

        this._currentBackButton = back;
        this._currentBackButton.onclick = function(event) {
          _this.shouldGoBack && _this.shouldGoBack();
        }
      }

      if(shouldShow && !this._currentBackButton.parentNode) {
        // Prepend the back button
        this.el.insertBefore(this._currentBackButton, this.el.firstChild);
      } else if(!shouldShow && this._currentBackButton.parentNode) {
        // Remove the back button if it's there
        this._currentBackButton.parentNode.removeChild(this._currentBackButton);
      }
    }
  };

})(ionic);