Fix handling of circular references in event data when using debug mode

Fixes #95

index.js

@@ -216,7 +216,12 @@ class Emittery {
 
 		if (!this.debug.logger) {
 			this.debug.logger = (type, debugName, eventName, eventData) => {
-				eventData = JSON.stringify(eventData);
+				try {
+					// TODO: Use https://github.com/sindresorhus/safe-stringify when the package is more mature. Just copy-paste the code.
+					eventData = JSON.stringify(eventData);
+				} catch {
+					eventData = `Object with the following keys failed to stringify: ${Object.keys(eventData).join(',')}`;
+				}
 
 				if (typeof eventName === 'symbol') {
 					eventName = eventName.toString();

test/index.js

@@ -1210,3 +1210,17 @@ test('isDebug can be turned on for and instance without using the constructor',
 	t.is(eventStore[2].debugName, 'testEmitter');
 	t.is(eventStore[2].eventData, 'test data');
 });
+
+test('debug mode - handles circular references in event data', async t => {
+	const emitter = new Emittery({
+		debug: {
+			name: 'testEmitter',
+			enabled: true
+		}
+	});
+
+	const data = {};
+	data.circular = data;
+
+	await t.notThrowsAsync(emitter.emit('test', data));
+});