Refactor events

Removes some duplication between xhr/event_target and dom/event_target.

Implement 'once' option of addEventListener.

Author: karlseguin

src/browser/dom/event_target.zig

@@ -41,68 +41,14 @@ pub const EventTarget = struct {
 
     // JS funcs
     // --------
-
-    const AddEventListenerOpts = union(enum) {
-        opts: Opts,
-        capture: bool,
-
-        const Opts = struct {
-            capture: ?bool,
-            // We ignore this property. It seems to be largely used to help the
-            // browser make certain performance tweaks (i.e. the browser knows
-            // that the listener won't call preventDefault() and thus can safely
-            // run the default as needed).
-            passive: ?bool,
-            once: ?bool, // currently does nothing
-            signal: ?bool, // currently does nothing
-        };
-    };
-
     pub fn _addEventListener(
         self: *parser.EventTarget,
         typ: []const u8,
         listener: EventHandler.Listener,
-        opts_: ?AddEventListenerOpts,
+        opts: ?EventHandler.Opts,
         page: *Page,
     ) !void {
-        var capture = false;
-        if (opts_) |opts| {
-            switch (opts) {
-                .capture => |c| capture = c,
-                .opts => |o| {
-                    // Done this way so that, for common cases that _only_ set
-                    // capture, i.e. {captrue: true}, it works.
-                    // But for any case that sets any of the other flags, we
-                    // error. If we don't error, this function call would succeed
-                    // but the behavior might be wrong. At this point, it's
-                    // better to be explicit and error.
-                    if (o.once orelse false) return error.NotImplemented;
-                    if (o.signal orelse false) return error.NotImplemented;
-                    capture = o.capture orelse false;
-                },
-            }
-        }
-
-        const cbk = (try listener.callback(self)) orelse return;
-
-        // check if event target has already this listener
-        const lst = try parser.eventTargetHasListener(
-            self,
-            typ,
-            capture,
-            cbk.id,
-        );
-        if (lst != null) {
-            return;
-        }
-        const eh = try EventHandler.init(page.arena, cbk);
-
-        try parser.eventTargetAddEventListener(
-            self,
-            typ,
-            &eh.node,
-            capture,
-        );
+        _ = try EventHandler.register(page.arena, self, typ, listener, opts);
     }
 
     const RemoveEventListenerOpts = union(enum) {

src/browser/dom/mutation_observer.zig

@@ -63,37 +63,37 @@ pub const MutationObserver = struct {
 
         // register node's events
         if (options.childList or options.subtree) {
-            try parser.eventTargetAddEventListener(
+            _ = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMNodeInserted",
                 &observer.event_node,
                 false,
             );
-            try parser.eventTargetAddEventListener(
+            _ = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMNodeRemoved",
                 &observer.event_node,
                 false,
             );
         }
         if (options.attr()) {
-            try parser.eventTargetAddEventListener(
+            _ = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMAttrModified",
                 &observer.event_node,
                 false,
             );
         }
         if (options.cdata()) {
-            try parser.eventTargetAddEventListener(
+            _ = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMCharacterDataModified",
                 &observer.event_node,
                 false,
             );
         }
         if (options.subtree) {
-            try parser.eventTargetAddEventListener(
+            _ = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMSubtreeModified",
                 &observer.event_node,

src/browser/events/event.zig

@@ -138,8 +138,11 @@ pub const Event = struct {
 };
 
 pub const EventHandler = struct {
+    once: bool,
+    capture: bool,
     callback: Function,
     node: parser.EventNode,
+    listener: *parser.EventListener,
 
     const Env = @import("../env.zig").Env;
     const Function = Env.Function;
@@ -159,15 +162,73 @@ pub const EventHandler = struct {
         }
     };
 
-    pub fn init(allocator: Allocator, callback: Function) !*EventHandler {
+    pub const Opts = union(enum) {
+        flags: Flags,
+        capture: bool,
+
+        const Flags = struct {
+            once: ?bool,
+            capture: ?bool,
+            // We ignore this property. It seems to be largely used to help the
+            // browser make certain performance tweaks (i.e. the browser knows
+            // that the listener won't call preventDefault() and thus can safely
+            // run the default as needed).
+            passive: ?bool,
+            signal: ?bool, // currently does nothing
+        };
+    };
+
+    pub fn register(
+        allocator: Allocator,
+        target: *parser.EventTarget,
+        typ: []const u8,
+        listener: Listener,
+        opts_: ?Opts,
+    ) !?*EventHandler {
+        var once = false;
+        var capture = false;
+        if (opts_) |opts| {
+            switch (opts) {
+                .capture => |c| capture = c,
+                .flags => |f| {
+                    // Done this way so that, for common cases that _only_ set
+                    // capture, i.e. {captrue: true}, it works.
+                    // But for any case that sets any of the other flags, we
+                    // error. If we don't error, this function call would succeed
+                    // but the behavior might be wrong. At this point, it's
+                    // better to be explicit and error.
+                    if (f.signal orelse false) return error.NotImplemented;
+                    once = f.once orelse false;
+                    capture = f.capture orelse false;
+                },
+            }
+        }
+
+        const callback = (try listener.callback(target)) orelse return null;
+
+        // check if event target has already this listener
+        if (try parser.eventTargetHasListener(target, typ, capture, callback.id) != null) {
+            return null;
+        }
+
         const eh = try allocator.create(EventHandler);
         eh.* = .{
+            .once = once,
+            .capture = capture,
             .callback = callback,
             .node = .{
                 .id = callback.id,
                 .func = handle,
             },
+            .listener = undefined,
         };
+
+        eh.listener = try parser.eventTargetAddEventListener(
+            target,
+            typ,
+            &eh.node,
+            capture,
+        );
         return eh;
     }
 
@@ -182,6 +243,17 @@ pub const EventHandler = struct {
         self.callback.tryCall(void, .{ievent}, &result) catch {
             log.debug(.event, "handle callback error", .{ .err = result.exception, .stack = result.stack });
         };
+
+        if (self.once) {
+            const target = (parser.eventTarget(event) catch return).?;
+            const typ = parser.eventType(event) catch return;
+            parser.eventTargetRemoveEventListener(
+                target,
+                typ,
+                self.listener,
+                self.capture,
+            ) catch {};
+        }
     }
 };
 
@@ -282,4 +354,13 @@ test "Browser.Event" {
         .{ "document.dispatchEvent(new Event('count'))", "true" },
         .{ "nb", "0" },
     }, .{});
+
+    try runner.testCases(&.{
+        .{ "nb = 0; function cbk(event) { nb ++; }", null },
+        .{ "document.addEventListener('count', cbk, {once: true})", null },
+        .{ "document.dispatchEvent(new Event('count'))", "true" },
+        .{ "document.dispatchEvent(new Event('count'))", "true" },
+        .{ "document.dispatchEvent(new Event('count'))", "true" },
+        .{ "nb", "1" },
+    }, .{});
 }

src/browser/netsurf.zig

@@ -615,7 +615,7 @@ pub fn eventTargetAddEventListener(
     typ: []const u8,
     node: *EventNode,
     capture: bool,
-) !void {
+) !*EventListener {
     const event_handler = struct {
         fn handle(event_: ?*Event, ptr_: ?*anyopaque) callconv(.C) void {
             const ptr = ptr_ orelse return;
@@ -634,6 +634,8 @@ pub fn eventTargetAddEventListener(
     const s = try strFromData(typ);
     const err = eventTargetVtable(et).add_event_listener.?(et, s, listener, capture);
     try DOMErr(err);
+
+    return listener.?;
 }
 
 pub fn eventTargetHasListener(

src/browser/page.zig

@@ -273,7 +273,7 @@ pub const Page = struct {
         const doc = parser.documentHTMLToDocument(html_doc);
 
         const document_element = (try parser.documentGetDocumentElement(doc)) orelse return error.DocumentElementError;
-        try parser.eventTargetAddEventListener(
+        _ = try parser.eventTargetAddEventListener(
             parser.toEventTarget(parser.Element, document_element),
             "click",
             &self.window_clicked_event_node,

src/browser/xhr/event_target.zig

@@ -48,17 +48,14 @@ pub const XMLHttpRequestEventTarget = struct {
     ) !?Function {
         const target = @as(*parser.EventTarget, @ptrCast(self));
 
-        const callback = (try listener.callback(target)) orelse return null;
-        const eh = try EventHandler.init(alloc, callback);
-        try parser.eventTargetAddEventListener(
-            target,
-            typ,
-            &eh.node,
-            false,
-        );
-
-        return callback;
+        // The only time this can return null if the listener is already
+        // registered. But before calling `register`, all of our functions
+        // remove any existing listener, so it should be impossible to get null
+        // from this function call.
+        const eh = (try EventHandler.register(alloc, target, typ, listener, null)) orelse unreachable;
+        return eh.callback;
     }
+
     fn unregister(self: *XMLHttpRequestEventTarget, typ: []const u8, cbk_id: usize) !void {
         const et = @as(*parser.EventTarget, @ptrCast(self));
         // check if event target has already this listener