You can add some code in 'onDrag' and 'onStopDrag' events to limit the boundaries of the draggable area.
<script>
function constrain(e){
var d = e.data;
if (d.left < 0){d.left = 0}
if (d.top < 0){d.top = 0}
if (d.left + $(d.target).outerWidth() > $(d.parent).width()){
d.left = $(d.parent).width() - $(d.target).outerWidth();
}
if (d.top + $(d.target).outerHeight() > $(d.parent).height()){
d.top = $(d.parent).height() - $(d.target).outerHeight();
}
}
</script>
<div style="position:relative;overflow:hidden;border:1px solid #ccc;width:400px;height:400px">
<div class="easyui-draggable" style="width:100px;height:100px;border:1px solid #ccc" data-options="
onDrag: function(e){
constrain(e);
},
onStopDrag: function(e){
constrain(e);
$(this).css(e.data);
}
">
</div>
</div>