Change Headers multiple value handling for spec compatibility

Consider this Headers object:

    var h = new Headers()
    h.append('accept', 'text/html')
    h.append('accept', 'text/plain')
    h.append('content-type', 'application/json')

Before:

- `h.get('accept')` returned `text/html`
- `h.getAll('accept')` returned an array of values
- `h.forEach` (and other iterables) did distinct iterations for each
  value of the same header

Now:

- `h.get('accept')` returns `text/html,text/plain`
- `h.getAll()` is no more
- `h.forEach` (and other iterables) now only do one iteration for each
  headers name, regardless of multiple values

This is in accordance with Section 3.1.2 of the spec, "combine" concept.

The updated tests currently break in Chrome and Firefox when exercising
the native implementation because their implementation is outdated. The
implementation in Edge is more correct, but the tests still fail there
because its implementation combines values with `, ` (notice the space)
rather than `,`.

fetch.js

@@ -73,41 +73,33 @@
   Headers.prototype.append = function(name, value) {
     name = normalizeName(name)
     value = normalizeValue(value)
-    var list = this.map[name]
-    if (!list) {
-      list = []
-      this.map[name] = list
-    }
-    list.push(value)
+    var oldValue = this.map[name]
+    this.map[name] = oldValue ? oldValue+','+value : value
   }
 
   Headers.prototype['delete'] = function(name) {
     delete this.map[normalizeName(name)]
   }
 
   Headers.prototype.get = function(name) {
-    var values = this.map[normalizeName(name)]
-    return values ? values[0] : null
-  }
-
-  Headers.prototype.getAll = function(name) {
-    return this.map[normalizeName(name)] || []
+    name = normalizeName(name)
+    return this.has(name) ? this.map[name] : null
   }
 
   Headers.prototype.has = function(name) {
     return this.map.hasOwnProperty(normalizeName(name))
   }
 
   Headers.prototype.set = function(name, value) {
-    this.map[normalizeName(name)] = [normalizeValue(value)]
+    this.map[normalizeName(name)] = normalizeValue(value)
   }
 
   Headers.prototype.forEach = function(callback, thisArg) {
-    Object.getOwnPropertyNames(this.map).forEach(function(name) {
-      this.map[name].forEach(function(value) {
-        callback.call(thisArg, value, name, this)
-      }, this)
-    }, this)
+    for (var name in this.map) {
+      if (this.map.hasOwnProperty(name)) {
+        callback.call(thisArg, this.map[name], name, this)
+      }
+    }
   }
 
   Headers.prototype.keys = function() {

test/test.js

@@ -122,8 +122,8 @@ suite('Headers', function() {
     original.append('Content-Type', 'text/html')
 
     var headers = new Headers(original)
-    assert.deepEqual(['application/json', 'text/plain'], headers.getAll('Accept'))
-    assert.deepEqual(['text/html'], headers.getAll('Content-Type'))
+    assert.equal(headers.get('Accept'), 'application/json,text/plain')
+    assert.equal(headers.get('Content-type'), 'text/html')
   })
   test('headers are case insensitive', function() {
     var headers = new Headers({'Accept': 'application/json'})
@@ -141,9 +141,7 @@ suite('Headers', function() {
   test('appends values to existing header name', function() {
     var headers = new Headers({'Accept': 'application/json'})
     headers.append('Accept', 'text/plain')
-    assert.equal(headers.getAll('Accept').length, 2)
-    assert.equal(headers.getAll('Accept')[0], 'application/json')
-    assert.equal(headers.getAll('Accept')[1], 'text/plain')
+    assert.equal(headers.get('Accept'), 'application/json,text/plain')
   })
   test('sets header name and value', function() {
     var headers = new Headers()
@@ -167,20 +165,10 @@ suite('Headers', function() {
     assert.isFalse(headers.has('Content-Type'))
     assert.isNull(headers.get('Content-Type'))
   })
-  test('returns list on getAll when header found', function() {
-    var headers = new Headers({'Content-Type': 'application/json'})
-    assert.isArray(headers.getAll('Content-Type'))
-    assert.equal(headers.getAll('Content-Type').length, 1)
-    assert.equal(headers.getAll('Content-Type')[0], 'application/json')
-  })
-  test('returns empty list on getAll when no header found', function() {
-    var headers = new Headers()
-    assert.isArray(headers.getAll('Content-Type'))
-    assert.equal(headers.getAll('Content-Type').length, 0)
-  })
   test('converts field name to string on set and get', function() {
     var headers = new Headers()
     headers.set(1, 'application/json')
+    assert.isTrue(headers.has('1'))
     assert.equal(headers.get(1), 'application/json')
   })
   test('converts field value to string on set and get', function() {
@@ -191,8 +179,8 @@ suite('Headers', function() {
     assert.equal(headers.get('X-CSRF-Token'), 'undefined')
   })
   test('throws TypeError on invalid character in field name', function() {
-    assert.throws(function() { new Headers({'<Accept>': ['application/json']}) }, TypeError)
-    assert.throws(function() { new Headers({'Accept:': ['application/json']}) }, TypeError)
+    assert.throws(function() { new Headers({'<Accept>': 'application/json'}) }, TypeError)
+    assert.throws(function() { new Headers({'Accept:': 'application/json'}) }, TypeError)
     assert.throws(function() {
       var headers = new Headers()
       headers.set({field: 'value'}, 'application/json')
@@ -209,10 +197,9 @@ suite('Headers', function() {
       results.push({value: value, key: key, object: object})
     })
 
-    assert.equal(results.length, 3)
-    assert.deepEqual({key: 'accept', value: 'application/json', object: headers}, results[0])
-    assert.deepEqual({key: 'accept', value: 'text/plain', object: headers}, results[1])
-    assert.deepEqual({key: 'content-type', value: 'text/html', object: headers}, results[2])
+    assert.equal(results.length, 2)
+    assert.deepEqual({key: 'accept', value: 'application/json,text/plain', object: headers}, results[0])
+    assert.deepEqual({key: 'content-type', value: 'text/html', object: headers}, results[1])
   })
   featureDependent(test, !nativeFirefox, 'forEach accepts second thisArg argument', function() {
     var headers = new Headers({'Accept': 'application/json'})
@@ -229,7 +216,6 @@ suite('Headers', function() {
 
     var iterator = headers.keys()
     assert.deepEqual({done: false, value: 'accept'}, iterator.next())
-    assert.deepEqual({done: false, value: 'accept'}, iterator.next())
     assert.deepEqual({done: false, value: 'content-type'}, iterator.next())
     assert.deepEqual({done: true, value: undefined}, iterator.next())
   })
@@ -240,8 +226,7 @@ suite('Headers', function() {
     headers.append('Content-Type', 'text/html')
 
     var iterator = headers.values()
-    assert.deepEqual({done: false, value: 'application/json'}, iterator.next())
-    assert.deepEqual({done: false, value: 'text/plain'}, iterator.next())
+    assert.deepEqual({done: false, value: 'application/json,text/plain'}, iterator.next())
     assert.deepEqual({done: false, value: 'text/html'}, iterator.next())
     assert.deepEqual({done: true, value: undefined}, iterator.next())
   })
@@ -252,8 +237,7 @@ suite('Headers', function() {
     headers.append('Content-Type', 'text/html')
 
     var iterator = headers.entries()
-    assert.deepEqual({done: false, value: ['accept', 'application/json']}, iterator.next())
-    assert.deepEqual({done: false, value: ['accept', 'text/plain']}, iterator.next())
+    assert.deepEqual({done: false, value: ['accept', 'application/json,text/plain']}, iterator.next())
     assert.deepEqual({done: false, value: ['content-type', 'text/html']}, iterator.next())
     assert.deepEqual({done: true, value: undefined}, iterator.next())
   })