Event related polyfills (for evergreen browsers)

polyfill.Events.js

if( !('SubmitEvent' in self && 'submitter' in SubmitEvent.prototype) ){
// polyfill SubmitEvent.submitter (a Safari issue as-of 2021)
// https://developer.mozilla.org/docs/Web/API/SubmitEvent
	const submitter = Symbol.for('submitter');
	Event[ submitter ] = null;
	const submitterSelector = 'input[type=submit], input[type=image], input[type=button], button';

	Object.defineProperty(Event.prototype, 'submitter', {
		get: function(){
			if('submit' === this.type){
				let node = Event[ submitter ];
				const form = this.target;
				if(!node || !form.contains(node)){
					node = form.querySelector(submitterSelector);
				}
				// always return a node, default as though form.submit called
				return node || form;
			}
			return undefined;
		},
		set: function(value){
			if('submit' === this.type){
				this.submitter = value;
			}
		}
	});
	self.addEventListener('click', function polyfill_SubmitEvent_submitter_click(event){
		const node = event.composedPath()[0];
		const closest = node.closest?.(submitterSelector) ?? null;
		Event[ submitter ] = closest;
	}, true);
}