[builtins] Implement Array.prototype.reduce in the CSA

test/mjsunit/array-reduce.js

 // Copyright 2009 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
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@@ skipping 390 matching lines @@
             [1, 2, 1, arrayPlus, 3],
             [3, 3, 3, arrayPlus, 6],
            ], arrayPlus, sum, 0);
 
 testReduce("reduceRight", "ArrayWithNonElementPropertiesReduceRight", 6,
            [[0, 3, 3, arrayPlus, 3],
             [3, 2, 1, arrayPlus, 5],
             [5, 1, 0, arrayPlus, 6],
            ], arrayPlus, sum, 0);
 
+// Test passing undefined as initial value (to test missing parameter
+// detection).
+[1].reduce((a, b) => { assertEquals(a, undefined); assertEquals(b, 1) },
+           undefined);
+[1, 2].reduce((a, b) => { assertEquals(a, 1); assertEquals(b, 2); });
+[1].reduce((a, b) => { assertTrue(false); });
 
 // Test error conditions:
 
 var exception = false;
 try {
   [1].reduce("not a function");
 } catch (e) {
   exception = true;
   assertTrue(e instanceof TypeError,
              "reduce callback not a function not throwing TypeError");
@@ skipping 103 matching lines @@
 
 var arr = [];
 Object.defineProperty(arr, "0", { get: function() { delete this[0] },
   configurable: true });
 assertEquals(undefined, arr.reduce(function(val) { return val }));
 
 var arr = [];
 Object.defineProperty(arr, "0", { get: function() { delete this[0] },
   configurable: true});
 assertEquals(undefined, arr.reduceRight(function(val) { return val }));