testDirectProxySetFailure.js

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// Test handling of false return from a handler.set() hook.

load(libdir + "asserts.js");

var obj = {x: 1};

var p = new Proxy(obj, {

    set(target, key, value, receiver) { return false; }

});

// Failing to set a property is a no-op in non-strict code.

assertEq(p.x = 2, 2);

assertEq(obj.x, 1);

// It's a TypeError in strict mode code.

assertThrowsInstanceOf(() => { "use strict"; p.x = 2; }, TypeError);

assertEq(obj.x, 1);

// Even if the value doesn't change.

assertThrowsInstanceOf(() => { "use strict"; p.x = 1; }, TypeError);

assertEq(obj.x, 1);

// Even if the target property doesn't already exist.

assertThrowsInstanceOf(() => { "use strict"; p.z = 1; }, TypeError);

assertEq("z" in obj, false);

// [].sort() mutates its operand only by doing strict [[Set]] calls.

var arr = ["not", "already", "in", "order"];

var p2 = new Proxy(arr, {

    set(target, key, value, receiver) { return false; }

});

assertThrowsInstanceOf(() => p2.sort(), TypeError);

assertDeepEq(arr, ["not", "already", "in", "order"]);