Pipe

Make a pipable

Pipable is a object, which have a method named .pipe(fun,...args).

You can get a new pipable object as fellow ways:

const {
  Pipe,
  pipe,
  from,
  _
} = require('./pipe.js')

test('make pipable', () => {
  const properties = ['valueOf', 'pipe', 'map', "promise_rescue"].sort();
  const keys = Object.keys.bind(Object);
  expect(keys(Pipe(1)).sort()).toMatchObject(properties);
  expect(keys(pipe(1)).sort()).toMatchObject(properties);
  expect(keys(from(1)).sort()).toMatchObject(properties);
  expect(keys(from(1).pipe(a => a + 1)).sort()).toMatchObject(properties);
})

As then snippet showed, a pipable object have methods as fellow:

• pipable.valueOf() :

  Get the v you want to pipe to other function.

  So pipe(a).valueOf() === a is always true:

  test('pipe(any).valueOf() == any', () => { expect(pipe(1).valueOf() == 1).toBe(true) expect(pipe("hello").valueOf() == "hello").toBe(true); expect(pipe(true).valueOf() == true).toBe(true); expect(pipe(false).valueOf() == false).toBe(true); let str = new String('Hello'); expect(pipe(str).valueOf() == str).toBe(true); expect(pipe(null).valueOf() == null).toBe(true); expect(pipe(undefined).valueOf() == undefined).toBe(true); let a = { hello: "a" }; expect(pipe(a).valueOf() == a).toBe(true) })

If a is primary type but neither null nor undefined then pipe(a) == a is true.

test('pipe(primary) == primary', () => {
  expect(pipe(1) == 1).toBe(true)
  expect(pipe("hello") == "hello").toBe(true);
  expect(pipe(true) == true).toBe(true);
  expect(pipe(false) == false).toBe(true);
  let str = new String('Hello')
  expect(pipe(str) == str).toBe(false);
  expect(pipe(null) == null).toBe(false);
  expect(pipe(undefined) == undefined).toBe(false);
  let a = { hello: "a" };
  expect(pipe(a) == a).toBe(false);
})

• pipable.pipe(fun,...args) : Return a pipable object.

  fun is a function, args are the rest arguments you want pipe to fun.

  • If args do not included placeholder _, fun will be called as fun(...[v,...args]).

  • If args included one and only one placeholder _, pipable.valueOf() will instead of the placehoder, and fun will be called as fun(...args).

• pipable.map(fun,...args) : pipable.map is the alias of pipable.pipe.

• pipable.promise_rescue(fun,...args): return a new pipable object.

  • when the pipable.vlaueOf() is a promise and the promise is reject, the reject reason will pipe to fun.
  • when pipeable.valueOf() is not a promise, fun will been skiped and return copy of pipable.

Use placeholder set which argument of fun take the piped value

test('pipe with placeholder', () => {
  let fn = jest.fn((a, b, c) => a + b + c);
  let z = pipe('a').pipe(fn, 'b', 'c');
  expect(fn).not.toHaveBeenCalled();
  expect(z == 'abc').toBe(true);
  expect(fn).toBeCalledWith('a', 'b', 'c');
  z = pipe("2").pipe(fn, "1", _, "3");
  expect(z == '123').toBe(true);
  expect(fn).toBeCalledWith('1', '2', '3');
  z = pipe('e').pipe(fn, 'a', 'b', 'c', 'd', _);
  expect(z == 'abc');
  expect(fn).toHaveBeenLastCalledWith('a', 'b', 'c', 'd', 'e');
})

pipable.pipe(fun,...args) keep pipable object immutable.

pipable.pipe(fn,...args) will return a new pipable object,don't change the old one.

test('pipable is independ', () => {
  let a = 1;
  let fn1 = jest.fn(a => a + 1);
  let fn2 = jest.fn((b, c) => b + c);
  let pipable0 = pipe(a);
  let pipable1 = pipable0.pipe(fn1);
  expect(pipable1 == a + 1).toBe(true);
  expect(pipable0.valueOf()).toBe(a);
  let pipable2 = pipable1.pipe(fn2, 'c');
  expect(pipable2 == '2c').toBe(true);
  expect(pipable1.valueOf()).toBe(a + 1);
})

pipable.pipe(fn,...args) is lazy

Call pipeable.pipe(fn,...args) do not call fn, but pipable.valueOf() will call the fn if there have one. As fellow show:

test(`pipable is layze`, () => {
  const fn = jest.fn(a => a + 1);
  let pipable0 = pipe(1);
  let ret = pipable0.pipe(fn).pipe(fn).pipe(fn);
  expect(fn).not.toHaveBeenCalled();
  expect(ret.valueOf()).toBe(1 + 1 + 1 + 1);
  expect(fn.mock.calls).toMatchObject([[1], [2], [3]]);
})

pipable<Promise>.pipe(fn,...args)

If the value of a pipable is a Promise, pipable.pipe(fn) pipe the resolve value of the promise to fn, and return a new promise pipable.

Examaples

test('pipe promise resolve ', (done) => {
  let a = from(Promise.resolve(1));
  expect(a.valueOf()).toBeInstanceOf(Promise);
  let fn = jest.fn(a => a + 1);
  let ret = a.pipe(fn).
    promise_rescue(fn).//skip
    pipe(fn).valueOf();
  expect(ret).toBeInstanceOf(Promise);
  ret.then(() => {
    expect(fn.mock.calls).toMatchObject([[1], [2]]);
    done();
  });
})

pipable<Promise>.promise_rescue:

Return a new pipable.

If value of pipable<Promise> is reject, this method can rescue from the error.

test('pipe promise reject', (done) => {
  let a = from(Promise.reject('hello'));
  let fn1 = jest.fn(a => 'fn1');
  let fn2 = jest.fn(a => 'fn2');
  let fn3 = jest.fn(a => "fn3");
  let promise = a.pipe(fn1).//skip
    promise_rescue(fn2).//call
    pipe(fn3).valueOf();
  expect(promise).toBeInstanceOf(Promise);

  promise.then(
    (a) => {
      expect(fn1).not.toHaveBeenCalled();
      expect(fn2).toHaveBeenCalledWith('hello');
      expect(fn3).toHaveBeenCalledWith('fn2');
      expect(a).toBe('fn3');
      done();
    },
    (error) => {
      console.error(error);
      expect('not run to here').toBe('but it is here');
    }
  )
})

pipable.inspect(fn, ...args)

Return a new pipable.

Run then function fn, ignor the return value of fn, so the value of the pipable will keep not change.

The purpose of this method is helpfully debuging the pipeable chain.