JSTests/test262/test/built-ins/Array/prototype/map/15.4.4.19-9-12.js

// Copyright (c) 2012 Ecma International.  All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.

/*---
esid: sec-array.prototype.map
es5id: 15.4.4.19-9-12
description: >
    Array.prototype.map - returns an empty array if 'length' is 0
    (subclassed Array, length overridden with [])
---*/

        function Foo() { }
        Foo.prototype = [1, 2, 3];
        var f = new Foo();

        f.length = [];

        // objects inherit the default valueOf method of the Object object;
        // that simply returns the itself. Since the default valueOf() method
        // does not return a primitive value, ES next tries to convert the object
        // to a number by calling its toString() method and converting the
        // resulting string to a number.
        //
        // The toString( ) method on Array converts the array elements to strings,
        // then returns the result of concatenating these strings, with commas in
        // between. An array with no elements converts to the empty string, which
        // converts to the number 0. If an array has a single element that is a
        // number n, the array converts to a string representation of n, which is
        // then converted back to n itself. If an array contains more than one element,
        // or if its one element is not a number, the array converts to NaN.

        function cb() { }
        var a = Array.prototype.map.call(f, cb);

assert(Array.isArray(a), 'Array.isArray(a) !== true');
assert.sameValue(a.length, 0, 'a.length');