Here is my Blank Widget.js for the WAB. This should work for you as a sample.
define([
"jimu/BaseWidget",
"dojo/_base/declare",
"dojo/on",
"dojo/dom-construct",
"dojo/dom",
"dojo/dom-style",
"dojo/query",
"dojo/dom-class",
"dojo/dom-attr",
"dojo/keys",
"dojo/store/Memory",
"dojo/_base/fx",
"dojo/_base/window",
"dojo/dom-geometry",
],
function (BaseWidget,
declare, on, domConstruct, dom, domStyle, query, domClass, domAttr, keys, Memory, fx, win, domGeom)
{
return declare([BaseWidget], {
baseClass: 'sc-widget-',
name: 'SC-BlankWidget',
constructor: function ()
{
this.inherited(arguments);
},
startup: function ()
{
this.inherited(arguments);
alert('hello World')
},
});
});