Use Symbol.toStringTag instead of adding toString to the prototype

Closes #21.

lib/constructs/interface.js

@@ -66,11 +66,9 @@ const IteratorPrototype = Object.create(utils.IteratorPrototype, {
     enumerable: true,
     configurable: true
   },
-  toString: {
-    value: function toString() {
-      return "[object ${this.name}Iterator]";
-    },
-    writable: true,
+  [Symbol.toStringTag]: {
+    value: "${this.name}Iterator",
+    writable: false,
     enumerable: false,
     configurable: true
   }
@@ -357,30 +355,6 @@ Interface.prototype.generateAttributes = function () {
   }
 };
 
-Interface.prototype.generateToString = function () {
-  let hasToString = false;
-  for (const member of this.idl.members) {
-    if (member.stringifier || member.name === "toString") {
-      hasToString = true;
-    }
-  }
-  if (!hasToString) {
-    this.str += `\n${this.name}.prototype.toString = function () {
-  if (this === ${this.name}.prototype) {
-    return "[object ${this.name}Prototype]";
-  }`;
-  if (this.idl.inheritance) {
-    this.str += `
-  return ${this.idl.inheritance}.interface.prototype.toString.call(this);`;
-  } else {
-    this.str += `
-  return this[impl].toString();`;
-  }
-  this.str += `
-};\n`;
-  }
-};
-
 Interface.prototype.generateSymbols = function () {
   const unscopables = {};
   for (const member of this.idl.members) {
@@ -393,6 +367,7 @@ Interface.prototype.generateSymbols = function () {
     this.str += `
 ${this.name}.prototype[Symbol.unscopables] = ${JSON.stringify(unscopables, null, '  ')};\n`;
   }
+  this.str += `\n${this.name}.prototype[Symbol.toStringTag] = ${JSON.stringify(this.name)};\n`;
 };
 
 Interface.prototype.generate = function () {
@@ -410,7 +385,6 @@ module.exports = {
   this.generateMixins();
 
   this.generateOperations();
-  this.generateToString();
   this.generateAttributes();
 
   this.generateRequires();