google-apps-script: No "source" field on event trigger - google-apps-script

Question

I've set up a trigger for submission of a Google form to run one of my Google scripts:
ScriptApp.newTrigger('onFormSubmitted')
.forForm(form).onFormSubmit().create();
My onFormSubmitted function gets triggered, but the event argument supplied to the function has no source attribute. It has 3 of the 4 fields that the documentation says it should have.
So how should I get a reference to the form that triggered this event?
TMI
function onFormSubmitted(data, arg) {
log(8, data['triggerUid'], -1) // => 1874727473075378640
log(9, data['authMode'], -1) // => FULL
log(10, data['response'], -1) // => FormResponse
log(11, data['source'], -1) // => undefined
}

Answer 1

As mentioned in the documentation for the event object, if the script is not bound, then there is no associated source property. You can overcome this by storing the form id in properties using the trigger uid. Then in your form submit code, use the trigger uid to obtain the proper Form.
function getFormId_(triggerId) {
const store = PropertiesService.getScriptProperties();
var formId = store.getProperty(triggerId);
if (!formId) console.warn("No form ID found for trigger ID '" + triggerId);
return formId;
}
function createSubmitTrigger_(form, functionName) {
const formId = form.getId();
const trigger = ScriptApp.newTrigger(functionName).forForm(form)
.onFormSubmit()
.create();
const store = PropertiesService.getScriptProperties();
store.setProperty(trigger.getUniqueId(), formId);
}
function myFormSubmit(e) {
const form = FormApp.openById(getFormId_(e.triggerUid));
...
}
It's possible this approach (store & retrieve) can be backwards-applied, though this will depend on how the triggers have previously been configured - you cannot programmatically (or otherwise) interact with others' triggers.
function storeAll() { // Run once (more is ok too, will just overwrite existing keys).
function cb(acc, t, i, allVals) { // callback for Array#reduce
acc[t.getUniqueId()] = t.getTriggerSourceId();
return acc;
}
const newProps = ScriptApp.getProjectTriggers().reduce(cb, {});
PropertiesService.getScriptProperties().setProperties(newProps);
}
References
Trigger class
getProjectTriggers is only for current user
Array#reduce