ladybird/Libraries/LibJS/Tests/functions/function-default-parameters.js

test("single default parameter", () => {
  function func(a = 6) {
    return typeof a;
  }

  const arrowFunc = (a = 6) => typeof a;

  expect(func()).toBe("number");
  expect(func(5)).toBe("number");
  expect(func(undefined)).toBe("number");
  expect(func(false)).toBe("boolean");
  expect(func(null)).toBe("object");
  expect(func({})).toBe("object");

  expect(arrowFunc()).toBe("number");
  expect(arrowFunc(5)).toBe("number");
  expect(arrowFunc(undefined)).toBe("number");
  expect(arrowFunc(false)).toBe("boolean");
  expect(arrowFunc(null)).toBe("object");
  expect(arrowFunc({})).toBe("object");
});

test("two parameters, second one is default", () => {
  function func(a, b = 1) {
    return a + b;
  }

  const arrowFunc = (a, b = 1) => a + b;

  expect(func(4, 5)).toBe(9);
  expect(func(4)).toBe(5);
  expect(func(4, undefined)).toBe(5);
  expect(func()).toBeNaN();

  expect(arrowFunc(4, 5)).toBe(9);
  expect(arrowFunc(4)).toBe(5);
  expect(arrowFunc(4, undefined)).toBe(5);
  expect(arrowFunc()).toBeNaN();
});

test("two parameters, first one is default", () => {
  function func(a = 5, b) {
    return a + b;
  }

  const arrowFunc = (a = 5, b) => a + b;

  expect(func(4, 5)).toBe(9);
  expect(func(undefined, 4)).toBe(9);
  expect(func()).toBeNaN();

  expect(arrowFunc(4, 5)).toBe(9);
  expect(arrowFunc(undefined, 4)).toBe(9);
  expect(arrowFunc()).toBeNaN();
});

test("default parameter references a previous parameter", () => {
  function func(a, b = a) {
    return a + b;
  }

  const arrowFunc = (a, b = a) => a + b;

  expect(func(4, 5)).toBe(9);
  expect(func(4)).toBe(8);
  expect(func("hf")).toBe("hfhf");
  expect(func(true)).toBe(2);
  expect(func()).toBeNaN();

  expect(arrowFunc(4, 5)).toBe(9);
  expect(arrowFunc(4)).toBe(8);
  expect(arrowFunc("hf")).toBe("hfhf");
  expect(arrowFunc(true)).toBe(2);
  expect(arrowFunc()).toBeNaN();
});

test("parameter with a function default value", () => {
  function func(
    a = function () {
      return 5;
    }
  ) {
    return a();
  }

  const arrowFunc = (
    a = function () {
      return 5;
    }
  ) => a();

  expect(func()).toBe(5);
  expect(
    func(function () {
      return 10;
    })
  ).toBe(10);
  expect(func(() => 10)).toBe(10);

  expect(arrowFunc()).toBe(5);
  expect(
    arrowFunc(function () {
      return 10;
    })
  ).toBe(10);
  expect(arrowFunc(() => 10)).toBe(10);
});

test("parameter with an arrow function default vlaue", () => {
  function func(a = () => 5) {
    return a();
  }

  const arrowFunc = (a = () => 5) => a();

  expect(func()).toBe(5);
  expect(
    func(function () {
      return 10;
    })
  ).toBe(10);
  expect(func(() => 10)).toBe(10);
  expect(arrowFunc()).toBe(5);
  expect(
    arrowFunc(function () {
      return 10;
    })
  ).toBe(10);
  expect(arrowFunc(() => 10)).toBe(10);
});

test("parameter with an object default value", () => {
  function func(a = { foo: "bar" }) {
    return a.foo;
  }

  const arrowFunc = (a = { foo: "bar" }) => a.foo;

  expect(func()).toBe("bar");
  expect(func({ foo: "baz" })).toBe("baz");
  expect(arrowFunc()).toBe("bar");
  expect(arrowFunc({ foo: "baz" })).toBe("baz");
});