If you want to use JavaScript to stop workflow for item, we can use JSOM code to achieve it, the following function for your reference.
function terminateWorkflow(listId, itemId, subId) {
var context = SP.ClientContext.get_current();
var workflowServicesManager = SP.WorkflowServices.WorkflowServicesManager.newObject(context, context.get_web());
var workflowInstanceService = workflowServicesManager.getWorkflowInstanceService();
var wfInstances = workflowInstanceService.enumerateInstancesForListItem(listId, itemId);
context.load(wfInstances);
context.executeQueryAsync(
function (sender, args) {
var instancesEnum = wfInstances.getEnumerator();
while (instancesEnum.moveNext()) {
var instance = instancesEnum.get_current();
if (instance.get_workflowSubscriptionId().toString() == subId.toLowerCase()) {
workflowInstanceService.terminateWorkflow(instance);
context.executeQueryAsync(
function (sender, args) {
console.log("Termination Successful");
},
function (sender, args) {
console.log("Failed to terminate workflow.");
console.log("Error: " + args.get_message() + "\n" + args.get_stackTrace());
}
);
}
}
},
function (sender, args) {
console.log("Failed to load instances.");
console.log("Error: " + args.get_message() + "\n" + args.get_stackTrace());
}
);
};
More information is here: Workflow Services CSOM and JSOM API components
We can also use PowerShell with CSOM to achieve it.
Stop/Start workflow for SharePoint Online using PowerShell Script