maybe-baby
2.x will be maintained, however, if possible for your repository, you should opt to use TypeScript's optional chaining, which was introduced in 3.7
Install
npm install --save maybe-babyyarn add maybe-baby
Getting Started
What if we need the zipCode of the user below, which lives on the address object?
const user = {
email: 'foo@bar.com',
address: null,
name: {
first: 'John',
last: null,
middle: null
}
};Accessing it via dot notation will result in an error:
const zipCode = user.address.zipCode; // Uncaught TypeError: Cannot read property 'zipCode' of undefinedPossible Solutions?
- Write some ugly null checks that don't scale well:
const getZipCode = (user) => {
if (user !== null && user !== undefined) {
if (user.address !== null && user.address !== undefined) {
return user.address.zipCode
}
}
}-
Use
_.get()or something similar, but these libraries have large footprints, and most likely won't be implementing the monadic structure. -
Wait for optional chaining to be approved in ECMA, or use babel-plugin-transform-optional-chaining.
-
Use TypeScript's optional chaining
A Better Solution?
- Use
maybe-babyto minimize defensive coding:
import Maybe from 'maybe-baby';
// Use a function getter
const getZipCode = (user) => Maybe.of(() => user.address.zipCode).join();Now we can safely get the zipCode without worrying about the shape of the object, or encountering TypeErrors:
const zipCode = getZipCode(user);
console.log(zipCode); // undefinedDocs
Documentation generated via JSDoc.
Migrating from 1.x to 2.x
Breaking changes were introduced in 2.0.0; the following redundant function were removed.
Maybe.of() can replicate the behavior of
prop,props, andpath.
prop(val: string | number)
const obj = Maybe.of({
foo: {
bar: [123, 456]
}
});
// Incorrect
const bar = obj.prop("foo").join(); // { bar: [123, 456] }
// Correct
Maybe.of(() => obj.join().foo).join(); // { bar: [123, 456] }
// Incorrect
obj
.prop("foo")
.prop("bar")
.prop(1)
.join(); // 456
// Correct
Maybe.of(() => obj.join().foo.bar[1]).join() // 456
props(...args)
const obj = Maybe.of({
foo: 'bar',
baz: [1,2,3]
});
// Incorrect
obj.props('baz', 0).join(); // 1
// Correct
Maybe.of(() => obj.join().baz[0]).join(); // 1
props(val: string)
const obj = Maybe.of({
foo: 'bar',
baz: [1,2,3]
});
// Incorrect
obj.path('baz.0').join() // 1
// Correct
Maybe.of(() => obj.join().baz[0]).join(); // 1API
Check out the API below, or the complete documentation.
of(val: unknown | OfTypeFunc<T>)
Accepts a value of any type, and returns a monad:
const str = Maybe.of('foo');
const num = Maybe.of(123);
const bool = Maybe.of(true);
const obj = Maybe.of({});
const arr = Maybe.of([]);
const empty = Maybe.of(null);
const undef = Maybe.of(undefined);Accepts a function, and sets the function's return value as the monad's value, returns a monad.
If the function results in an error, the monad's value is set to
undefined.
type OfTypeFunc<T> = () => T;
const user = {};
const mZipCode = Maybe.of(() => user.address.zipCode);
console.log(mZipCode.join()); // undefined
isJust(): boolean
Returns true if the value is not null or undefined:
Maybe.of(123).isJust(); // true
Maybe.of(null).isJust(); // false
isNothing(): boolean
Returns true if the value is null or undefined:
Maybe.of(123).isNothing(); // false
Maybe.of(null).isNothing(); // true
join(): T
Returns the value:
Maybe.of(123).join(); // 123
Maybe.of(null).join(); // null
orElse(defaultValue: unknown): Maybe
Chain to the end of a monad to return as the default value if isNothing() is true:
Maybe.of(undefined)
.orElse('No Value')
.join(); // 'No Value'
map(transform: (val: T) => T | Maybe<T>): Maybe
Apply a transformation to the monad, and return a new monad:
const val = 1;
const newVal = Maybe.of(val).map(val => val + 1);
newVal.join(); // 2;
chain(chain: (val: T) => Maybe<T>): Maybe
Chain together functions that return Maybe monads:
function addOne (val) {
return Maybe.of(val + 1);
}
const three = Maybe.of(1)
.chain(addOne)
.chain(addOne);
three.join(); // 3Credit
Credit to James Sinclair for writing The Marvellously Mysterious JavaScript Maybe Monad.