ladybird/Userland/Libraries/LibJS/Tests/builtins/Array/array-length-setter.js

describe("errors", () => {
    test("invalid array length value", () => {
        var a = [1, 2, 3];
        [undefined, "foo", -1, Infinity, -Infinity, NaN].forEach(value => {
            expect(() => {
                a.length = value;
            }).toThrowWithMessage(RangeError, "Invalid array length");
            expect(a).toHaveLength(3);
        });
    });
});

describe("normal behavior", () => {
    test("extend array by setting length", () => {
        var a = [1, 2, 3];
        a.length = 5;
        expect(a).toEqual([1, 2, 3, undefined, undefined]);
    });

    test("truncate array by setting length", () => {
        var a = [1, 2, 3];
        a.length = 2;
        expect(a).toEqual([1, 2]);
        a.length = 0;
        expect(a).toEqual([]);
    });

    test("length value is coerced to number if possible", () => {
        var a = [1, 2, 3];
        a.length = "42";
        expect(a).toHaveLength(42);
        a.length = [];
        expect(a).toHaveLength(0);
        a.length = true;
        expect(a).toHaveLength(1);
    });

    test("setting a huge array length", () => {
        var a = [];
        a.length = 0x80000000;
        expect(a.length).toEqual(0x80000000);

        var b = [];
        b.length = 0x80000001;
        expect(b.length).toEqual(0x80000001);
    });

    test("should not remove non-configurable values", () => {
        var a = [1, undefined, 3];
        Object.defineProperty(a, 1, { configurable: false, value: 2 });
        expect(a.length).toEqual(3);

        expect((a.length = 1)).toEqual(1);
        expect(a.length).toEqual(2);
        expect(a[1]).toEqual(2);
    });
});