test/mjsunit/delete-non-configurable.js

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// Delete elements of a String object.
var TIPLI = "tipli"
var so = new String(TIPLI);
var length = so.length;

for (var i = 0; i < length; i++) {
  assertFalse(delete so[i]);
  assertThrows("'use strict'; delete so[i];", TypeError);
  assertFalse(delete so[i.toString()]);
  assertThrows("'use strict'; delete so[i.toString()];", TypeError);
}

assertEquals(length, so.length);
assertEquals(new String(TIPLI), so);

// Delete elements of an Array.
var arr = new Array(length);

for (var i = 0; i < length; i++) {
  arr[i] = i;
  Object.defineProperty(arr, i, { configurable: false });
}

for (var i = 0; i < length; i++) {
  assertFalse(delete arr[i]);
  assertThrows("'use strict'; delete arr[i];", TypeError);
  assertFalse(delete arr[i.toString()]);
  assertThrows("'use strict'; delete arr[i.toString()];", TypeError);
  assertEquals(i, arr[i]);
}

assertEquals(length, arr.length);
assertTrue(delete arr[length]);

// Delete an element of an Object.
var INDEX = 28;
var obj = new Object();

obj[INDEX] = TIPLI;
Object.defineProperty(obj, INDEX, { configurable: false });

assertFalse(delete obj[INDEX]);
assertThrows("'use strict'; delete obj[INDEX];", TypeError);
assertFalse(delete obj[INDEX.toString()]);
assertThrows("'use strict'; delete obj[INDEX.toString()];", TypeError);
assertEquals(TIPLI, obj[INDEX]);
assertTrue(delete arr[INDEX+1]);