Trying to Start SharePoint workflow from code

Question

I have what may be a familiar piece of code for starting a SharePoint 2013 workflow, except mine fails with an error of "Error: Value cannot be null. Parameter name: subscription undefined." The log I have to check for this never triggers so I'm not sure why the value suddenly isn't being passed properly.

<a href="#" onclick="startWorkflow('2', '947ABD00-0EB4-454D-B561-89CBF6205581')">New Quick Start on 2</a>//using specific item ID to test

<script type="text/javascript" src="/_layouts/15/sp.runtime.js"></script>
<script type="text/javascript" src="/_layouts/15/sp.js"></script>
<script type="text/javascript" src="/_layouts/15/sp.workflowservices.js"></script>

<script type="text/javascript">
function startWorkflow(itemID, subID) {

var context = SP.ClientContext.get_current();
var web = context.get_web();

var wfServiceManager = SP.WorkflowServices.WorkflowServicesManager.newObject(context, web);

var subService = wfServiceManager.getWorkflowSubscriptionService()

context.load(subService);

context.executeQueryAsync(
    function(sender, args){
        var subscription = subService.getSubscription(subID);

if(subscription == null){console.log("Null Subscription")}

        if(subscription){

        console.log("Subscription load success. Attempting to start workflow.");        
        var inputParameters = {};

        wfServiceManager.getWorkflowInstanceService().startWorkflowOnListItem(subscription, itemID, new Object());
        }

        context.executeQueryAsync(
            function(sender, args){ console.log("Successfully starting workflow."); },
            function(sender, args){ 
                console.log("Failed to start workflow.");
                console.log("Error: " + args.get_message() + "\n" + args.get_stackTrace());
            }
        );
    },
    function(sender,args){
        console.log("Failed to load subscription.");
        console.log("Error: " + args.get_message() + "\n" + args.get_stackTrace());
    }
);
}
</script>

Answer 1

Alas everytime you publish a Workflow it gets a new (GU)ID,

So starting by Workflow ID is a pain

You can start by Name (Note, this came from a button in a View, I deleted lines before pasting, so there might be typos)

event.preventDefault();
var TR = GetAncestor(this, 'TR');
var itemID = TR.id.split(',')[1];
var wfName = 'YOUR_WORKFLOW_TITLE_GOES_HERE';
SP.SOD.executeFunc('sp.workflowservices.js', 'SP.WorkflowServices.WorkflowServicesManager',
    function () {
        var ctx = new SP.ClientContext.get_current(),
            wfsManager = SP.WorkflowServices.WorkflowServicesManager.newObject(ctx, ctx.get_web()),
            wfSubs = wfsManager.getWorkflowSubscriptionService().enumerateSubscriptionsByList(_spPageContextInfo.pageListId);
        ctx.load(wfSubs);
        ctx.executeQueryAsync(function () {
            wfsEnum = wfSubs.getEnumerator();
            while (wfsEnum.moveNext()) {
                var wfSub = wfsEnum.get_current();
                if (wfSub.get_name() === wfName) {
                    wfsManager.getWorkflowInstanceService().startWorkflowOnListItem(wfSub, itemID, new Object());
                    SP.UI.Notify.addNotification('Init Workflow: ' + wfName + ' on item: ' + itemID, false);
                }
            }
        },function(e){console.error(e)});
    });

Answer 2

Building on the solutions provided by others, here's the code I was able to use. NOTE: You need to have your workflow set to "Allow this workflow to be started manually."

/**
*   Starts a SharePoint 2013 Workflow on a particular list item.
*   Params:
*       workflowName: The name of the Workflow
*       listGUID: the GUID of the list
*       itemId: the ID of the list item
*/  
function startListWorkflow(workflowName, listGUID, itemId){
    SP.SOD.executeFunc("sp.js", "SP.ClientContext" , function(){
        SP.SOD.registerSod('sp.workflowservices.js', SP.Utilities.Utility.getLayoutsPageUrl('sp.workflowservices.js'));
        SP.SOD.executeFunc('sp.workflowservices.js', "SP.WorkflowServices.WorkflowServicesManager", 
            function(){
                var ctx = new SP.ClientContext.get_current(),
                wfsManager = SP.WorkflowServices.WorkflowServicesManager.newObject(ctx, ctx.get_web()),
                wfSubs = wfsManager.getWorkflowSubscriptionService().enumerateSubscriptionsByList(listGUID);
                ctx.load(wfSubs);
                ctx.executeQueryAsync(function () {
                    wfsEnum = wfSubs.getEnumerator();
                    while (wfsEnum.moveNext()) {
                        var wfSub = wfsEnum.get_current();
                        if (wfSub.get_name() === workflowName) {
                            var initiationParams = {}; 
                            wfsManager.getWorkflowInstanceService().startWorkflowOnListItem(wfSub, itemId, initiationParams);
                            ctx.executeQueryAsync(
                               function (sender, args) {
                                    console.log("Successfully started workflow.");
                               },
                               function (sender, args) {
                                    console.log("Failed to start the workflow.");
                                    console.log("Error: " + args.get_message() + "\n" + args.get_stackTrace());
                               }
                           );
                        }
                    }
                },function(e){
                    console.error(e)
                });
            }
        );
    });         
}