unite webidl stringification

lib/web/fetch/webidl.js

@@ -136,7 +136,7 @@ webidl.util.ConvertToInt = function (V, bitLength, signedness, opts = {}) {
     ) {
       throw webidl.errors.exception({
         header: 'Integer conversion',
-        message: `Could not convert ${V} to an integer.`
+        message: `Could not convert ${webidl.util.Stringify(V)} to an integer.`
       })
     }
 
@@ -216,6 +216,21 @@ webidl.util.IntegerPart = function (n) {
   return r
 }
 
+webidl.util.Stringify = function (V) {
+  const type = webidl.util.Type(V)
+
+  switch (type) {
+    case 'Symbol':
+      return `Symbol(${V.description})`
+    case 'Object':
+      return JSON.stringify(V)
+    case 'String':
+      return V.length ? V : '""'
+    default:
+      return `${V}`
+  }
+}
+
 // https://webidl.spec.whatwg.org/#es-sequence
 webidl.sequenceConverter = function (converter) {
   return (V, Iterable) => {
@@ -324,7 +339,7 @@ webidl.interfaceConverter = function (i) {
     if (opts.strict !== false && !(V instanceof i)) {
       throw webidl.errors.exception({
         header: i.name,
-        message: `Expected ${V} to be an instance of ${i.name}.`
+        message: `Expected ${JSON.stringify(V)} to be an instance of ${i.name}.`
       })
     }
 
@@ -515,8 +530,8 @@ webidl.converters.ArrayBuffer = function (V, opts = {}) {
     !types.isAnyArrayBuffer(V)
   ) {
     throw webidl.errors.conversionFailed({
-      prefix: `${V}`,
-      argument: `${V}`,
+      prefix: webidl.util.Stringify(V),
+      argument: webidl.util.Stringify(V),
       types: ['ArrayBuffer']
     })
   }
@@ -556,7 +571,7 @@ webidl.converters.TypedArray = function (V, T, opts = {}) {
   ) {
     throw webidl.errors.conversionFailed({
       prefix: `${T.name}`,
-      argument: `${V}`,
+      argument: webidl.util.Stringify(V),
       types: [T.name]
     })
   }
@@ -629,7 +644,7 @@ webidl.converters.BufferSource = function (V, opts = {}) {
     return webidl.converters.DataView(V, opts, { ...opts, allowShared: false })
   }
 
-  throw new TypeError(`Could not convert ${V} to a BufferSource.`)
+  throw new TypeError(`Could not convert ${webidl.util.Stringify(V)} to a BufferSource.`)
 }
 
 webidl.converters['sequence<ByteString>'] = webidl.sequenceConverter(

test/webidl/converters.js

@@ -183,3 +183,22 @@ test('ByteString', () => {
              'index 7 has a value of 256 which is greater than 255.'
   })
 })
+
+test('webidl.util.Stringify', (t) => {
+  const pairs = [
+    [Object.create(null), '{}'],
+    [{ a: 'b' }, '{"a":"b"}'],
+    [Symbol('sym'), 'Symbol(sym)'],
+    [Symbol.iterator, 'Symbol(Symbol.iterator)'], // well-known symbol
+    [true, 'true'],
+    [0, '0'],
+    ['hello', 'hello'],
+    ['', '""'],
+    [null, 'null'],
+    [undefined, 'undefined']
+  ]
+
+  for (const [value, expected] of pairs) {
+    assert.deepStrictEqual(webidl.util.Stringify(value), expected)
+  }
+})

test/websocket/messageevent.js

@@ -103,7 +103,7 @@ test('test/parallel/test-worker-message-port.js', () => {
   })
   assert.throws(() => new MessageEvent('message', { source: {} }), {
     constructor: TypeError,
-    message: 'MessagePort: Expected [object Object] to be an instance of MessagePort.'
+    message: 'MessagePort: Expected {} to be an instance of MessagePort.'
   })
   assert.throws(() => new MessageEvent('message', { ports: 0 }), {
     constructor: TypeError,
@@ -117,7 +117,7 @@ test('test/parallel/test-worker-message-port.js', () => {
     new MessageEvent('message', { ports: [{}] })
   , {
     constructor: TypeError,
-    message: 'MessagePort: Expected [object Object] to be an instance of MessagePort.'
+    message: 'MessagePort: Expected {} to be an instance of MessagePort.'
   })
 
   assert(new MessageEvent('message') instanceof Event)

types/webidl.d.ts

@@ -62,6 +62,11 @@ interface WebidlUtil {
    * @see https://webidl.spec.whatwg.org/#abstract-opdef-converttoint
    */
   IntegerPart (N: number): number
+
+  /**
+   * Stringifies {@param V}
+   */
+  Stringify (V: any): string
 }
 
 interface WebidlConverters {