Training material to onboard people on using fp-ts efficiently.
The exercises consist of unimplemented functions and their associated failing tests.
If needed, you can always refer to the exoN.solution.ts file where you will find the solution of the exercise.
But first, it is essential to understand why we are using fp-ts. We suggest you to read this article and then start the exercises.
After cloning the repository, setup the project by running
$ yarnTo run the tests, simply run
$ yarn testYou can also run them in watch mode:
$ yarn test:watchFinally, if you wish to only run the tests for a given exercise exoN, you can run the following:
$ yarn test[:watch] exoNThe exercises are organized into exoN folders and most of what is required to complete each is detailed in the comments.
For readability purpose, we replace ReaderTaskEither by rte
- Use
flowinstead ofpipewhen possibleWhy? Using flow reduces the amount of variables to declare in a method, hence the visibility and readability of the code
// Bad
const formatUserPhoneNumber = (user: User) =>
pipe(user, User.phoneNumber, User.formatPhoneNumber);
// Good
const formatUserPhoneNumber = flow(User.phoneNumber, User.formatPhoneNumber);- Avoid using
booleanmethodmatchwhen unecessaryWhy? boolean.match can lower the global understanding of a method and enforce nested pipes. Using classic
if/elseis often the best option
// Bad
const triggerEmailCampaign = ({
user,
...emailSettings
}: {
user: User} & EmailSettings) =>
pipe(
user.nationality === 'FR',
boolean.match(
() => triggerGlobalEmailCampaign({ to: user.email, emailSettings }),
() => triggerFrenchEmailCampaign({ to: user.email, emailSettings }),
),
);
// Good
const triggerEmailCampaign = ({
user,
...emailSettings
}: { user: User } & EmailSettings) => {
if (user.nationality === 'FR') {
return triggerFrenchEmailCampaign({ to: user.email, emailSettings });
}
return triggerGlobalEmailCampaign({ to: user.email, emailSettings });- Avoid nested pipes
Why? They lower global understanding of the code. We allow ourselves 2 levels of piping maximum per function and tend to do atomic functions instead
// Bad
export const convertDollarAmountInCountryCurrency = ({
countryName,
amountInDollar,
}: {
countryName: CountryName;
amountInDollar: number;
}) =>
pipe(
getCountryCode(countryName),
either.map(
countryCode =>
pipe(
getCountryCurrency(countryCode),
option.map(
flow(
convertFromDollarAmount(amountInDollar),
convertedAmount =>
console.log(
`converted amount for country ${countryCode} is ${convertedAmount}`,
),
),
),
),
),
),
);
// Good
export const convertDollarAmountInCountryCurrency = (amountInDollar: number) =>
flow(
getCountryCode,
either.map(convertDollarAmountToCountryCodeCurrency(amountInDollar)),
);
const convertDollarAmountToCountryCodeCurrency =
(amountInDollar: number) => (countryCode: CountryCode) =>
pipe(
getCountryCurrency(countryCode),
option.map(convertFromDollarAmount(amountInDollar)),
option.map(convertedAmount =>
console.log(
`converted amount for country ${countryCode} is ${convertedAmount}`,
),
),
);
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