Dgrid Checkbox Editor

HTML

<link rel="stylesheet" href="//ajax.googleapis.com/ajax/libs/dojo/1.10.4/dijit/themes/claro/claro.css">
<fieldset>
    <legend>Requirement</legend>
    <ul>
        <li>List Requirements</li>
    </ul>
</fieldset>
<div id="existingItemsGrid"></div>

CSS

.field-iceCream {
    width: 30px;
    text-align: center;
}
.field-iceCream input {
    width: auto;
}

JavaScript

var ui = {};
require({
    packages: [{
        name: 'dstore',
        location: '//cdn.rawgit.com/SitePen/dstore/v1.0.0'
    }]
}, ["dojo/ready", "dstore/Memory"],

function (ready, Memory) {
    ready(function () {
        var people = [{
            id: 1,
            firstName: "Billy",
            lastName: "Madison"
        }, {
            id: 2,
            firstName: "Happy",
            lastName: "Gilmore"
        }]
        ui.existingItemsGrid.set("collection", new Memory({
            data: people
        }));
       
    });
});

//Setup dgrids
require({
    packages: [{
        name: 'dgrid',
        location: '//cdn.rawgit.com/SitePen/dgrid/v0.4.0'
    }, {
        name: 'xstyle',
        location: '//cdn.rawgit.com/kriszyp/xstyle/v0.2.1'
    }, {
        name: 'put-selector',
        location: '//cdn.rawgit.com/kriszyp/put-selector/v0.3.6'
    }]
}, ["dojo/_base/declare", "dgrid/OnDemandGrid", "dgrid/Keyboard", "dgrid/Selection", "dgrid/extensions/ColumnResizer", "dgrid/Selector", "dgrid/extensions/DijitRegistry", "dojo/domReady!"],

function (declare, OnDemandGrid, Keyboard, Selection, Selector, ColumnResizer, DijitRegistry) {
    //define grid and create
    var Grid = declare([OnDemandGrid, Keyboard, Selection, ColumnResizer, DijitRegistry, Selector]);
    ui.existingItemsGrid = new Grid({
        columns: {
          	{ selector: 'checkbox' },
				  	{ label: 'Column 2', sortable: false },
					 	{ label: 'Column 3' }
            
        },
        selectionMode: "single",
        cellNavigation: false
    }, "existingItemsGrid");
});


//Parse widgets and setup ui variable for easy access
require(["dojo/parser", "dojo/ready", "dijit/registry", "dojo/_base/array"],

function (parser, ready, registry, array) {
    ready(100, function () {
        parser.parse().then(function () {
            array.forEach(registry.toArray(), function (instance) {
                ui[instance.id] = instance;
            });
        }).otherwise(function (e) {
...