v8/test/mjsunit/compiler/delete.js

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// Tests of unary delete in cases where it is always true or always false.

// In an effect context, expression is always true.
assertEquals(undefined, void (delete 0));
// In an effect context, expression is always false.
assertEquals(undefined, (function (x) { delete x; })(0));

// In a pure test context, expression is always true.
assertEquals(1, (delete 0) ? 1 : 2);
// In a pure test context, expression is always false.
assertEquals(2, (function (x) { return (delete x) ? 1 : 2; })(0));
// In a negated test context, expression is always false.
assertEquals(1, (function (x) { return !(delete x) ? 1 : 2; })(0));

// In a hybrid test/value context, expression is always true, value
// expected in accumulator.
assertEquals(3, 1 + ((delete 0) && 2));
// In a hybrid test/value context, expression is always false, value
// expected in accumulator.
assertEquals(false, (function (x) { return (delete x) && 2; })(0));
// In a hybrid test/value context, expression is always true, value
// expected on stack.
assertEquals(3, ((delete 0) && 2) + 1);
// In a hybrid test/value context, expression is always false, value
// expected on stack.
assertEquals(1, (function (x) { return ((delete x) && 2) + 1; })(0));

// In a hybrid value/test context, expression is always true, value
// expected in accumulator.
assertEquals(2, 1 + ((delete 0) || 2));
// In a hybrid value/test context, expression is always false, value
// expected in accumulator.
assertEquals(2, (function (x) { return (delete x) || 2; })(0));
// In a hybrid value/test context, expression is always true, value
// expected on stack.
assertEquals(2, ((delete 0) || 2) + 1);
// In a hybrid value/test context, expression is always false, value
// expected on stack.
assertEquals(3, (function (x) { return ((delete x) || 2) + 1; })(0));


// 'this' is not a Reference so delete returns true (see section 11.4.1,
// step 2 of ES 5.1).
assertEquals(true, delete this);
assertEquals(true, (function () { return delete this; })());