Improve “Illegal invocation” error messages

Author: ExE-Boss

lib/constructs/attribute.js

@@ -29,7 +29,7 @@ class Attribute {
 
     let brandCheck = `
       if (!exports.is(esValue)) {
-        throw new TypeError("Illegal invocation");
+        throw new TypeError("'$KEYWORD$ ${this.idl.name}' called on an object that does not implement interface ${this.interface.name}.");
       }
     `;
     let getterBody = `return utils.tryWrapperForImpl(esValue[implSymbol]["${this.idl.name}"]);`;
@@ -78,11 +78,13 @@ class Attribute {
     addMethod(this.idl.name, [], `
       ${promiseHandlingBefore}
       const esValue = this !== null && this !== undefined ? this : globalObject;
-      ${brandCheck}
+      ${brandCheck.replace("$KEYWORD$", "get")}
       ${getterBody}
       ${promiseHandlingAfter}
     `, "get", { configurable });
 
+    brandCheck = brandCheck.replace("$KEYWORD$", "set");
+
     if (!this.idl.readonly) {
       if (async) {
         throw new Error(`Illegal promise-typed attribute "${this.idl.name}" in interface "${this.interface.idl.name}"`);
@@ -159,7 +161,7 @@ class Attribute {
       addMethod("toString", [], `
         const esValue = this;
         if (!exports.is(esValue)) {
-          throw new TypeError("Illegal invocation");
+          throw new TypeError("'toString' called on an object that does not implement interface ${this.interface.name}.");
         }
 
         ${getterBody}

lib/constructs/iterable.js

@@ -20,8 +20,8 @@ class Iterable {
 
   generateFunction(key, kind) {
     this.interface.addMethod(this.interface.defaultWhence, key, [], `
-      if (!this || !exports.is(this)) {
-        throw new TypeError("Illegal invocation");
+      if (!exports.is(this)) {
+        throw new TypeError("'${key}' called on an object that does not implement interface ${this.interface.name}.");
       }
       return exports.createDefaultIterator(this, "${kind}");
     `);
@@ -35,8 +35,8 @@ class Iterable {
       this.generateFunction("entries", "key+value");
       this.interface.addProperty(whence, Symbol.iterator, `${this.interface.name}.prototype.entries`);
       this.interface.addMethod(whence, "forEach", ["callback"], `
-        if (!this || !exports.is(this)) {
-          throw new TypeError("Illegal invocation");
+        if (!exports.is(this)) {
+          throw new TypeError("'forEach' called on an object that does not implement interface ${this.interface.name}.");
         }
         if (arguments.length < 1) {
           throw new TypeError("Failed to execute 'forEach' on '${this.name}': 1 argument required, " +

lib/constructs/operation.js

@@ -85,7 +85,7 @@ class Operation {
       str += `
         const esValue = this !== null && this !== undefined ? this : globalObject;
         if (!exports.is(esValue)) {
-          throw new TypeError("Illegal invocation");
+          throw new TypeError("'${this.name}' called on an object that does not implement interface ${this.interface.name}.");
         }
       `;
     }