Edit in JSFiddle

$('[data-cs]').on('click', function(e){

    var $btn = $(this);
    
    bng.world.broadPhase.pxCellSize = parseFloat( $btn.attr('data-cs'), 10 );

});
<canvas id="ro-canvas" width="546" height="410"></canvas>

<!-- Vendor libraries -->
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/vendor/Stats.js"></script>

<!-- ro! -->
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.js"></script>
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.math.js"></script>
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.world.js"></script>
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.coltech.brute-force.js"></script>
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.coltech.hshg.js"></script>
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.coltech.spatial-grid.js"></script>
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.screen.js"></script>
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.entity.js"></script>
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/lib/ro.input.js"></script>

<!-- the demo -->
<script type="text/javascript" src="http://kirbysayshi.github.com/broad-phase-bng/examples/spatial-grid/orbit-sg-01.js"></script>

<div>
<input type="button" data-cs="1" value="Set cellSize = 1" />
<input type="button" data-cs="14.142" value="Set cellSize = Default" />
<input type="button" data-cs="50" value="Set cellSize = 50" />
</div>