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describe("[[Has]] trap normal behavior", () => {
test("forwarding when not defined in handler", () => {
expect("foo" in new Proxy({}, { has: null })).toBe(false);
expect("foo" in new Proxy({}, { has: undefined})).toBe(false);
expect("foo" in new Proxy({}, {})).toBe(false);
});
test("correct arguments supplied to trap", () => {
let o = {};
let p = new Proxy(o, {
has(target, prop) {
expect(target).toBe(o);
expect(prop).toBe("foo");
return true;
}
});
"foo" in p;
});
test("conditional return", () => {
let o = {};
let p = new Proxy(o, {
has(target, prop) {
if (target.checkedFoo)
return true;
if (prop === "foo")
target.checkedFoo = true;
return false;
}
});
expect("foo" in p).toBe(false);
expect("foo" in p).toBe(true);
});
});
describe("[[Has]] invariants", () => {
test("cannot return false if the property exists and is non-configurable", () => {
let o = {};
Object.defineProperty(o, "foo", { configurable: false });
p = new Proxy(o, {
has() {
return false;
}
});
expect(() => {
"foo" in p;
}).toThrowWithMessage(TypeError, "Proxy handler's has trap violates invariant: a property cannot be reported as non-existent if it exists on the target as a non-configurable property");
});
test("cannot return false if the property exists and the target is non-extensible", () => {
let o = {};
Object.defineProperty(o, "foo", { value: 10, configurable: true });
let p = new Proxy(o, {
has() {
return false;
}
});
Object.preventExtensions(o);
expect(() => {
"foo" in p;
}).toThrowWithMessage(TypeError, "Proxy handler's has trap violates invariant: a property cannot be reported as non-existent if it exists on the target and the target is non-extensible");
});
});
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