Lily/TempVariables2: nitpicking (#1796)

Safari 13 and 14 have enough users that they show up in the top 100 user
agents on clouddata.turbowarp.org so I'd like to keep as much alive
there for as long as possible. Thus avoid using ??= (Safari 14) or
Object.hasOwn (Safari 15.4).

Also includes ESLint rules, so that these are detected automatically
moving forward.

`ext_${extensionId}` is also a TurboWarp convention not a Scratch
convention

Probably at some point it makes sense to just adopt babel and compile
extensions down to Safari 12 but for now, avoiding significant
transformations is nice

eslint.config.js

@@ -111,6 +111,14 @@ module.exports = [
       ],
       'no-restricted-syntax': [
         'error',
+        {
+          selector: 'AssignmentExpression[operator="??="]',
+          message: 'x ??= y syntax is too new; use x = x ?? y intead'
+        },
+        {
+          selector: 'MemberExpression[object.name=Object][property.name=hasOwn]',
+          message: 'Object.hasOwn(...) is too new; use Object.prototype.hasOwnProperty.call(...) instead'
+        },
         {
           selector: 'CallExpression[callee.name=fetch]',
           message: 'Use Scratch.fetch() instead of fetch()'

extensions/Lily/TempVariables2.js

@@ -217,13 +217,17 @@
 
     setThreadVariable(args, util) {
       const thread = util.thread;
-      thread.variables ??= Object.create(null);
+      if (!thread.variables) {
+        thread.variables = Object.create(null);
+      }
       thread.variables[args.VAR] = args.STRING;
     }
 
     changeThreadVariable(args, util) {
       const thread = util.thread;
-      thread.variables ??= Object.create(null);
+      if (!thread.variables) {
+        thread.variables = Object.create(null);
+      }
       const vars = thread.variables;
       const prev = Scratch.Cast.toNumber(vars[args.VAR]);
       const next = Scratch.Cast.toNumber(args.NUM);
@@ -232,21 +236,29 @@
 
     getThreadVariable(args, util) {
       const thread = util.thread;
-      thread.variables ??= Object.create(null);
+      if (!thread.variables) {
+        thread.variables = Object.create(null);
+      }
       return thread.variables[args.VAR] ?? "";
     }
 
     threadVariableExists(args, util) {
       const thread = util.thread;
-      thread.variables ??= Object.create(null);
-      return Object.hasOwn(thread.variables, args.VAR);
+      if (!thread.variables) {
+        thread.variables = Object.create(null);
+      }
+      return Object.prototype.hasOwnProperty.call(thread.variables, args.VAR);
     }
 
     forEachThreadVariable(args, util) {
       const thread = util.thread;
-      thread.variables ??= Object.create(null);
+      if (!thread.variables) {
+        thread.variables = Object.create(null);
+      }
       const vars = thread.variables;
-      util.stackFrame.index ??= 0;
+      if (!Object.prototype.hasOwnProperty.call(util.stackFrame, "index")) {
+        util.stackFrame.index = 0;
+      }
       if (util.stackFrame.index < Number(args.NUM)) {
         util.stackFrame.index++;
         vars[args.VAR] = util.stackFrame.index;
@@ -256,7 +268,9 @@
 
     listThreadVariables(args, util) {
       const thread = util.thread;
-      thread.variables ??= Object.create(null);
+      if (!thread.variables) {
+        thread.variables = Object.create(null);
+      }
       return Object.keys(thread.variables).join(",");
     }
 
@@ -277,7 +291,10 @@
     }
 
     runtimeVariableExists(args) {
-      return Object.hasOwn(this.runtimeVariables, args.VAR);
+      return Object.prototype.hasOwnProperty.call(
+        this.runtimeVariables,
+        args.VAR
+      );
     }
 
     listRuntimeVariables(args, util) {
@@ -292,8 +309,9 @@
       this.runtimeVariables = Object.create(null);
     }
   }
-  // The expose format follows scratch's convention of `ext_${extensionId}`.
+  // The expose format follows TurboWarp's convention of `ext_${extensionId}`.
   // Expose the extension on runtime for others to use.
-  Scratch.vm.runtime.ext_lmsTempVars2 = new TempVars();
-  Scratch.extensions.register(Scratch.vm.runtime.ext_lmsTempVars2);
+  const extension = new TempVars();
+  Scratch.vm.runtime.ext_lmsTempVars2 = extension;
+  Scratch.extensions.register(extension);
 })(Scratch);