v8/test/mjsunit/delete-global-properties.js

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// Global properties declared with 'var' or 'function' should not be
// deleteable.
var tmp;
assertFalse(delete tmp);  // should be DONT_DELETE
assertTrue("tmp" in this);
function f() { return 1; }
assertFalse(delete f);  // should be DONT_DELETE
assertEquals(1, f());

// Check that deleting and reintroducing global variables works.
// Get into the IC case for storing to a deletable global property.
function introduce_x() { x = 42; }
for (var i = 0; i < 10; i++) introduce_x();
// Check that the property has been introduced.
assertTrue(this.hasOwnProperty('x'));
// Check that deletion works.
delete x;
assertFalse(this.hasOwnProperty('x'));
// Check that reintroduction works.
introduce_x();
assertTrue(this.hasOwnProperty('x'));