Source: http://sharepoint.stackexchange.com/questions/94648/sharepoint-2013-check-workflow-status-programmatically-javascript
var context = new SP.ClientContext.get_current();
var web = context.get_web();
var list = web.get_lists().getByTitle(listTitle);
var listItem = list.getItemById(listItemId);
context.load(listItem);
context.executeQueryAsync(
function() {
var workflowStatusField = listItem.get_parentList().get_fields().getByTitle(workflowTitle); //get workflow status field
var workflowStatusValue = listItem.get_item(workflowTitle); //get workflow status field value
success(workflowStatusValue);
},
error
);