test/mjsunit/array-concat.js

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/**
 * @fileoverview Test concat on small and large arrays
 */

var poses = [140, 4000000000];
while (pos = poses.shift()) {
  var a = new Array(pos);
  assertEquals(pos, a.length);
  a.push('foo');
  assertEquals(pos + 1, a.length);
  var b = ['bar'];
  var c = a.concat(b);
  assertEquals(pos + 2, c.length);
  assertEquals("undefined", typeof(c[pos - 1]));
  assertEquals("foo", c[pos]);
  assertEquals("bar", c[pos + 1]);

  // Can we fool the system by putting a number in a string?
  var onetwofour = "124";
  a[onetwofour] = 'doo';
  assertEquals(a[124], 'doo');
  c = a.concat(b);
  assertEquals(c[124], 'doo');

  // If we put a number in the prototype, then the spec says it should be
  // copied on concat.
  Array.prototype["123"] = 'baz';
  assertEquals(a[123], 'baz');

  c = a.concat(b);
  assertEquals(pos + 2, c.length);
  assertEquals("baz", c[123]);
  assertEquals("undefined", typeof(c[pos - 1]));
  assertEquals("foo", c[pos]);
  assertEquals("bar", c[pos + 1]);

  // When we take the number off the prototype it disappears from a, but
  // the concat put it in c itself.
  Array.prototype["123"] = undefined;
  assertEquals("undefined", typeof(a[123]));
  assertEquals("baz", c[123]);

  // If the element of prototype is shadowed, the element on the instance
  // should be copied, but not the one on the prototype.
  Array.prototype[123] = 'baz';
  a[123] = 'xyz';
  assertEquals('xyz', a[123]);
  c = a.concat(b);
  assertEquals('xyz', c[123]);

  // Non-numeric properties on the prototype or the array shouldn't get
  // copied.
  Array.prototype.moe = 'joe';
  a.ben = 'jerry';
  assertEquals(a["moe"], 'joe');
  assertEquals(a["ben"], 'jerry');
  c = a.concat(b);
  // ben was not copied
  assertEquals("undefined", typeof(c.ben));
  // moe was not copied, but we can see it through the prototype
  assertEquals("joe", c.moe);

  // When we take moe off the prototype it disappears from all arrays.
  Array.prototype.moe = undefined;
  assertEquals("undefined", typeof(c.moe));

  // Negative indeces don't get concated.
  a[-1] = 'minus1';
  assertEquals("minus1", a[-1]);
  assertEquals("undefined", typeof(a[0xffffffff]));
  c = a.concat(b);
  assertEquals("undefined", typeof(c[-1]));
  assertEquals("undefined", typeof(c[0xffffffff]));
  assertEquals(c.length, a.length + 1);

}

a = [];
c = a.concat('Hello');
assertEquals(1, c.length);
assertEquals("Hello", c[0]);
assertEquals("Hello", c.toString());

// Check that concat preserves holes.
var holey = [void 0,'a',,'c'].concat(['d',,'f',[0,,2],void 0])
assertEquals(9, holey.length);  // hole in embedded array is ignored
for (var i = 0; i < holey.length; i++) {
  if (i == 2 || i == 5) {
    assertFalse(i in holey);
  } else {
    assertTrue(i in holey);
  }
}