Use destructuring assignments for named parameters (#180)

lib/runtime/dart/_interceptors.js

 dart_library.library('dart/_interceptors', null, /* Imports */[
   "dart/_runtime",
   'dart/core',
   'dart/_internal',
   'dart/collection',
   'dart/math'
 ], /* Lazy imports */[
   'dart/_js_helper'
 ], function(exports, dart, core, _internal, collection, math, _js_helper) {
   'use strict';
@@ skipping 190 matching lines @@
         return new (_internal.IterableMixinWorkaround$(E))().skipWhile(this, test);
       }
       [dartx.reduce](combine) {
         dart.as(combine, dart.functionType(E, [E, E]));
         return dart.as(_internal.IterableMixinWorkaround.reduce(this, combine), E);
       }
       [dartx.fold](initialValue, combine) {
         dart.as(combine, dart.functionType(dart.dynamic, [dart.dynamic, E]));
         return _internal.IterableMixinWorkaround.fold(this, initialValue, combine);
       }
-      [dartx.firstWhere](test, opts) {
+      [dartx.firstWhere](test, {orElse = null} = {}) {
         dart.as(test, dart.functionType(core.bool, [E]));
-        let orElse = opts && 'orElse' in opts ? opts.orElse : null;
         dart.as(orElse, dart.functionType(E, []));
         return dart.as(_internal.IterableMixinWorkaround.firstWhere(this, test, orElse), E);
       }
-      [dartx.lastWhere](test, opts) {
+      [dartx.lastWhere](test, {orElse = null} = {}) {
         dart.as(test, dart.functionType(core.bool, [E]));
-        let orElse = opts && 'orElse' in opts ? opts.orElse : null;
         dart.as(orElse, dart.functionType(E, []));
         return dart.as(_internal.IterableMixinWorkaround.lastWhereList(this, test, orElse), E);
       }
       [dartx.singleWhere](test) {
         dart.as(test, dart.functionType(core.bool, [E]));
         return dart.as(_internal.IterableMixinWorkaround.singleWhere(this, test), E);
       }
       [dartx.elementAt](index) {
         return this[dartx.get](index);
       }
@@ skipping 108 matching lines @@
       }
       get [dartx.isEmpty]() {
         return this[dartx.length] == 0;
       }
       get [dartx.isNotEmpty]() {
         return !dart.notNull(this[dartx.isEmpty]);
       }
       toString() {
         return collection.ListBase.listToString(this);
       }
-      [dartx.toList](opts) {
-        let growable = opts && 'growable' in opts ? opts.growable : true;
+      [dartx.toList]({growable = true} = {}) {
         let list = this.slice();
         if (!dart.notNull(growable))
           JSArray$().markFixedList(dart.as(list, core.List));
         return JSArray$(E).typed(list);
       }
       [dartx.toSet]() {
         return core.Set$(E).from(this);
       }
       get [dartx.iterator]() {
         return new (_internal.ListIterator$(E))(this);
@@ skipping 638 matching lines @@
         return false;
       return other == this[dartx.substring](dart.notNull(this[dartx.length]) - dart.notNull(otherLength));
     }
     [dartx.replaceAll](from, to) {
       _js_helper.checkString(to);
       return dart.as(_js_helper.stringReplaceAllUnchecked(this, from, to), core.String);
     }
     [dartx.replaceAllMapped](from, convert) {
       return this[dartx.splitMapJoin](from, {onMatch: convert});
     }
-    [dartx.splitMapJoin](from, opts) {
-      let onMatch = opts && 'onMatch' in opts ? opts.onMatch : null;
-      let onNonMatch = opts && 'onNonMatch' in opts ? opts.onNonMatch : null;
+    [dartx.splitMapJoin](from, {onMatch = null, onNonMatch = null} = {}) {
       return dart.as(_js_helper.stringReplaceAllFuncUnchecked(this, from, onMatch, onNonMatch), core.String);
     }
     [dartx.replaceFirst](from, to, startIndex) {
       if (startIndex === void 0)
         startIndex = 0;
       _js_helper.checkString(to);
       _js_helper.checkInt(startIndex);
       if (dart.notNull(startIndex) < 0 || dart.notNull(startIndex) > dart.notNull(this[dartx.length])) {
         dart.throw(new core.RangeError.range(startIndex, 0, this[dartx.length]));
       }
@@ skipping 481 matching lines @@
   exports.JSString = JSString;
   exports.getInterceptor = getInterceptor;
   exports.JSBool = JSBool;
   exports.JSIndexable = JSIndexable;
   exports.JSMutableIndexable = JSMutableIndexable;
   exports.JSObject = JSObject;
   exports.JavaScriptObject = JavaScriptObject;
   exports.PlainJavaScriptObject = PlainJavaScriptObject;
   exports.UnknownJavaScriptObject = UnknownJavaScriptObject;
 });