js/src/tests/ecma_7/Destructuring/rest-parameter-aray-iterator.js


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/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// Destructuring rest arrays call the array iterator. This behaviour is
// observable when Array.prototype[Symbol.iterator] is overridden.

const oldArrayIterator = Array.prototype[Symbol.iterator];
try {
    let callCount = 0;
    Array.prototype[Symbol.iterator] = function() {
        callCount += 1;
        return oldArrayIterator.call(this);
    };

    // Array iterator called exactly once.
    function arrayIterCalledOnce(...[]) { }
    assertEq(callCount, 0);
    arrayIterCalledOnce();
    assertEq(callCount, 1);

    // Array iterator not called before rest parameter.
    callCount = 0;
    function arrayIterNotCalledBeforeRest(t = assertEq(callCount, 0), ...[]) { }
    assertEq(callCount, 0);
    arrayIterNotCalledBeforeRest();
    assertEq(callCount, 1);

    // Array iterator called when rest parameter is processed.
    callCount = 0;
    function arrayIterCalledWhenDestructuring(...[t = assertEq(callCount, 1)]) { }
    assertEq(callCount, 0);
    arrayIterCalledWhenDestructuring();
    assertEq(callCount, 1);
} finally {
    Array.prototype[Symbol.iterator] = oldArrayIterator;
}

if (typeof reportCompare === "function")
    reportCompare(0, 0);