lib: initialize instance members in class constructors

Since V8 snapshot does not currently support instance member
initialization, initialize them in ordianry class constructors
for now so that these classes can be included in the snapshot.
This may be reverted once
https://bugs.chromium.org/p/v8/issues/detail?id=10704
is fixed and backported.

PR-URL: #32984
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

lib/internal/event_target.js

@@ -42,32 +42,30 @@ function lazyNow() {
   return perf_hooks.performance.now();
 }
 
+// TODO(joyeecheung): V8 snapshot does not support instance member
+// initializers for now:
+// https://bugs.chromium.org/p/v8/issues/detail?id=10704
+const kType = Symbol('type');
+const kDefaultPrevented = Symbol('defaultPrevented');
+const kCancelable = Symbol('cancelable');
+const kTimestamp = Symbol('timestamp');
+const kBubbles = Symbol('bubbles');
+const kComposed = Symbol('composed');
+const kPropagationStopped = Symbol('propagationStopped');
 class Event {
-  #type = undefined;
-  #defaultPrevented = false;
-  #cancelable = false;
-  #timestamp = lazyNow();
-
-  // None of these are currently used in the Node.js implementation
-  // of EventTarget because there is no concept of bubbling or
-  // composition. We preserve their values in Event but they are
-  // non-ops and do not carry any semantics in Node.js
-  #bubbles = false;
-  #composed = false;
-  #propagationStopped = false;
-
-
   constructor(type, options) {
     if (arguments.length === 0)
       throw new ERR_MISSING_ARGS('type');
     if (options != null)
       validateObject(options, 'options');
     const { cancelable, bubbles, composed } = { ...options };
-    this.#cancelable = !!cancelable;
-    this.#bubbles = !!bubbles;
-    this.#composed = !!composed;
-    this.#type = `${type}`;
-    this.#propagationStopped = false;
+    this[kCancelable] = !!cancelable;
+    this[kBubbles] = !!bubbles;
+    this[kComposed] = !!composed;
+    this[kType] = `${type}`;
+    this[kDefaultPrevented] = false;
+    this[kTimestamp] = lazyNow();
+    this[kPropagationStopped] = false;
     // isTrusted is special (LegacyUnforgeable)
     Object.defineProperty(this, 'isTrusted', {
       get() { return false; },
@@ -87,10 +85,10 @@ class Event {
     });
 
     return `${name} ${inspect({
-      type: this.#type,
-      defaultPrevented: this.#defaultPrevented,
-      cancelable: this.#cancelable,
-      timeStamp: this.#timestamp,
+      type: this[kType],
+      defaultPrevented: this[kDefaultPrevented],
+      cancelable: this[kCancelable],
+      timeStamp: this[kTimestamp],
     }, opts)}`;
   }
 
@@ -99,20 +97,22 @@ class Event {
   }
 
   preventDefault() {
-    this.#defaultPrevented = true;
+    this[kDefaultPrevented] = true;
   }
 
   get target() { return this[kTarget]; }
   get currentTarget() { return this[kTarget]; }
   get srcElement() { return this[kTarget]; }
 
-  get type() { return this.#type; }
+  get type() { return this[kType]; }
 
-  get cancelable() { return this.#cancelable; }
+  get cancelable() { return this[kCancelable]; }
 
-  get defaultPrevented() { return this.#cancelable && this.#defaultPrevented; }
+  get defaultPrevented() {
+    return this[kCancelable] && this[kDefaultPrevented];
+  }
 
-  get timeStamp() { return this.#timestamp; }
+  get timeStamp() { return this[kTimestamp]; }
 
 
   // The following are non-op and unused properties/methods from Web API Event.
@@ -121,19 +121,19 @@ class Event {
 
   composedPath() { return this[kTarget] ? [this[kTarget]] : []; }
   get returnValue() { return !this.defaultPrevented; }
-  get bubbles() { return this.#bubbles; }
-  get composed() { return this.#composed; }
+  get bubbles() { return this[kBubbles]; }
+  get composed() { return this[kComposed]; }
   get eventPhase() {
     return this[kTarget] ? Event.AT_TARGET : Event.NONE;
   }
-  get cancelBubble() { return this.#propagationStopped; }
+  get cancelBubble() { return this[kPropagationStopped]; }
   set cancelBubble(value) {
     if (value) {
       this.stopPropagation();
     }
   }
   stopPropagation() {
-    this.#propagationStopped = true;
+    this[kPropagationStopped] = true;
   }
 
   static NONE = 0;
@@ -157,15 +157,8 @@ Object.defineProperty(Event.prototype, SymbolToStringTag, {
 // the linked list makes dispatching faster, even if adding/removing is
 // slower.
 class Listener {
-  next;
-  previous;
-  listener;
-  callback;
-  once;
-  capture;
-  passive;
-
   constructor(previous, listener, once, capture, passive) {
+    this.next = undefined;
     if (previous !== undefined)
       previous.next = this;
     this.previous = previous;
@@ -197,7 +190,9 @@ class EventTarget {
   // symbol as EventTarget may be used cross-realm. See discussion in #33661.
   static [kIsEventTarget] = true;
 
-  [kEvents] = new Map();
+  constructor() {
+    this[kEvents] = new Map();
+  }
 
   [kNewListener](size, type, listener, once, capture, passive) {}
   [kRemoveListener](size, type, listener, capture) {}
@@ -355,17 +350,22 @@ Object.defineProperty(EventTarget.prototype, SymbolToStringTag, {
   value: 'EventTarget',
 });
 
+const kMaxListeners = Symbol('maxListeners');
+const kMaxListenersWarned = Symbol('maxListenersWarned');
 class NodeEventTarget extends EventTarget {
   static defaultMaxListeners = 10;
 
-  #maxListeners = NodeEventTarget.defaultMaxListeners;
-  #maxListenersWarned = false;
+  constructor() {
+    super();
+    this[kMaxListeners] = NodeEventTarget.defaultMaxListeners;
+    this[kMaxListenersWarned] = false;
+  }
 
   [kNewListener](size, type, listener, once, capture, passive) {
-    if (this.#maxListeners > 0 &&
-        size > this.#maxListeners &&
-        !this.#maxListenersWarned) {
-      this.#maxListenersWarned = true;
+    if (this[kMaxListeners] > 0 &&
+        size > this[kMaxListeners] &&
+        !this[kMaxListenersWarned]) {
+      this[kMaxListenersWarned] = true;
       // No error code for this since it is a Warning
       // eslint-disable-next-line no-restricted-syntax
       const w = new Error('Possible EventTarget memory leak detected. ' +
@@ -382,12 +382,12 @@ class NodeEventTarget extends EventTarget {
 
   setMaxListeners(n) {
     validateInteger(n, 'n', 0);
-    this.#maxListeners = n;
+    this[kMaxListeners] = n;
     return this;
   }
 
   getMaxListeners() {
-    return this.#maxListeners;
+    return this[kMaxListeners];
   }
 
   eventNames() {