test/mjsunit/array-slice.js

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// Check that slicing array of holes keeps it as array of holes
(function() {
  var array = new Array(10);
  for (var i = 0; i < 7; i++) {
    var sliced = array.slice();
    assertEquals(array.length, sliced.length);
    assertFalse(0 in sliced);
  }
})();


// Check various variants of empty array's slicing.
(function() {
  for (var i = 0; i < 7; i++) {
    assertEquals([], [].slice(0, 0));
    assertEquals([], [].slice(1, 0));
    assertEquals([], [].slice(0, 1));
    assertEquals([], [].slice(-1, 0));
  }
})();


// Check various forms of arguments omission.
(function() {
  var array = new Array(7);

  for (var i = 0; i < 7; i++) {
    assertEquals(array, array.slice());
    assertEquals(array, array.slice(0));
    assertEquals(array, array.slice(undefined));
    assertEquals(array, array.slice("foobar"));
    assertEquals(array, array.slice(undefined, undefined));
  }
})();


// Check variants of negatives and positive indices.
(function() {
  var array = new Array(7);

  for (var i = 0; i < 7; i++) {
    assertEquals(7, array.slice(-100).length);
    assertEquals(3, array.slice(-3).length);
    assertEquals(3, array.slice(4).length);
    assertEquals(1, array.slice(6).length);
    assertEquals(0, array.slice(7).length);
    assertEquals(0, array.slice(8).length);
    assertEquals(0, array.slice(100).length);

    assertEquals(0, array.slice(0, -100).length);
    assertEquals(4, array.slice(0, -3).length);
    assertEquals(4, array.slice(0, 4).length);
    assertEquals(6, array.slice(0, 6).length);
    assertEquals(7, array.slice(0, 7).length);
    assertEquals(7, array.slice(0, 8).length);
    assertEquals(7, array.slice(0, 100).length);

    // Some exotic cases.

    obj = { toString: function() { throw 'Exception'; } };

    // More than 2 arguments:
    assertEquals(7, array.slice(0, 7, obj, null, undefined).length);

    // Custom conversion:
    assertEquals(1, array.slice({valueOf: function() { return 1; }},
                                {toString: function() { return 2; }}).length);

    // Throwing an exception in conversion:
    try {
      assertEquals(7, array.slice(0, obj).length);
      throw 'Should have thrown';
    } catch (e) {
      assertEquals('Exception', e);
    }
  }
})();


// Nasty: modify the array in ToInteger.
(function() {
  var array = [];
  var expected = []
  bad_guy = { valueOf: function() { array.push(array.length); return -1; } };

  for (var i = 0; i < 13; i++) {
    var sliced = array.slice(bad_guy);
    expected.push(i);
    assertEquals(expected, array);
    // According to the spec (15.4.4.10), length is calculated before
    // performing ToInteger on arguments.
    if (i == 0) {
      assertEquals([], sliced);  // Length was 0, nothing to get.
    } else {
      // Actually out of array [0..i] we get [i - 1] as length is i.
      assertEquals([i - 1], sliced);
    }
  }
})();


// Now check the case with array of holes and some elements on prototype.
// Note: that is important that this test runs before the next one
// as the next one tampers Array.prototype.
(function() {
  var len = 9;
  var array = new Array(len);

  var at3 = "@3";
  var at7 = "@7";

  for (var i = 0; i < 7; i++) {
    var array_proto = [];
    array_proto[3] = at3;
    array_proto[7] = at7;
    array.__proto__ = array_proto;

    assertEquals(len, array.length);
    for (var i = 0; i < array.length; i++) {
      assertEquals(array[i], array_proto[i]);
    }

    var sliced = array.slice();

    assertEquals(len, sliced.length);

    assertTrue(delete array_proto[3]);
    assertTrue(delete array_proto[7]);

    // Note that slice copies values from prototype into the array.
    assertEquals(array[3], undefined);
    assertFalse(array.hasOwnProperty(3));
    assertEquals(sliced[3], at3);
    assertTrue(sliced.hasOwnProperty(3));

    assertEquals(array[7], undefined);
    assertFalse(array.hasOwnProperty(7));
    assertEquals(sliced[7], at7);
    assertTrue(sliced.hasOwnProperty(7));

    // ... but keeps the rest as holes:
    array_proto[5] = "@5";
    assertEquals(array[5], array_proto[5]);
    assertFalse(array.hasOwnProperty(5));
  }
})();


// Now check the case with array of holes and some elements on prototype.
(function() {
  var len = 9;
  var array = new Array(len);

  var at3 = "@3";
  var at7 = "@7";

  for (var i = 0; i < 7; i++) {
    Array.prototype[3] = at3;
    Array.prototype[7] = at7;

    assertEquals(len, array.length);
    for (var i = 0; i < array.length; i++) {
      assertEquals(array[i], Array.prototype[i]);
    }

    var sliced = array.slice();

    assertEquals(len, sliced.length);

    assertTrue(delete Array.prototype[3]);
    assertTrue(delete Array.prototype[7]);

    // Note that slice copies values from prototype into the array.
    assertEquals(array[3], undefined);
    assertFalse(array.hasOwnProperty(3));
    assertEquals(sliced[3], at3);
    assertTrue(sliced.hasOwnProperty(3));

    assertEquals(array[7], undefined);
    assertFalse(array.hasOwnProperty(7));
    assertEquals(sliced[7], at7);
    assertTrue(sliced.hasOwnProperty(7));

    // ... but keeps the rest as holes:
    Array.prototype[5] = "@5";
    assertEquals(array[5], Array.prototype[5]);
    assertFalse(array.hasOwnProperty(5));
    assertEquals(sliced[5], Array.prototype[5]);
    assertFalse(sliced.hasOwnProperty(5));

    assertTrue(delete Array.prototype[5]);
  }
})();