exceptnomore

exceptnomore

Result and Optional types that will make your code exception-proof.

This library allows you to wrap Promises, async functions and normal functions in objects that will wrap those exceptions for a cleaner code with less try/catches and a better and more explicit Error Handling.

NPM Package

npm install exceptnomore

Full documentation:

• Result
• Optional

Highlights

Mapping and FlatMapping + if callbacks

Result.map

functionThatReturnsTheUserIdAsAResult()
    .map(id => getUserData(id))
    .ifOk(u => console.log(`Hello ${u.firstName}`))
    .ifErr(err => console.debug(err));
    // if err exists, it is the original Error returned by 'functionThatReturnsTheUserIdAsAResult'

Result.flatMap

functionThatReturnsTheUserIdAsAResult()
    .flatMap(id => mayFailGetUserData(id))
    .ifOk(u => console.log(`Hello ${u.firstName}`))
    .ifErr(err => console.debug(err));
    // if err exists, it is either the content of the Error Result of 'functionThatReturnsTheUserIdAsAResult'
    // or, if that successfully returned a userId, the Error Result of 'mayFailGetUserData'

flatMap and map rules also apply to the Optional type:

Optional.map

functionThatReturnsTheUserIdAsAnOptional()
    .map(id => getUserData(id))
    .ifPresent(u => console.log(`Hello ${u.firstName}`))
    .ifEmpty(() => console.debug('Not found'));

Optional.flatMap

functionThatReturnsTheUserIdAsAnOptional()
    .flatMap(id => mayNotFindUserData(id))
    .ifPresent(u => console.log(`Hello ${u.firstName}`))
    .ifEmpty(() => console.debug('Not found'));
    // the callback passed to ifEmpty gets called if
    // 'functionThatReturnsTheUserIdAsAnOptional'
    // or 'mayNotFindUserData' return an Empty Optional

Example use cases:

A function call that may throw an exception

Before - the caller is not aware that the function may throw an exception:

function evil(): number {
    const n = Math.random();
    if (n < .5) {
        throw new Error('Ooops');
    } else {
        return n;
    }
}

console.log(evil()); // This statement can crash

After - the return type explicitly tells the caller that the function may return an error (also telling the type of it):

function evil(): Result<number, Error> {
    const n = Math.random();
    if (n < .5) {
        return Result.err(new Error('Ooops'));
    } else {
        return Result.ok(n);
    }
}
evil().ifOk(n => console.log(n)); // This statement will never crash

// Also, if you want to manage the error
evil()
    .ifOk(n => console.log(n))
    .ifErr(e => console.debug(e));

// Or, to be more concise
evil().if(n => console.log(n), e => console.debug(e));

A function that may return the object we are looking for or null (for example, when looking for a record in a database table)

Before:

function find(id: number): { name: string }|null {
    return Math.random() * 10 < id
        ? null
        : { name: 'Test User' };
}

console.log(find(5).name); // Compiler error that forces you to handle the null case if you are using TypeScript, "TypeError: Cannot read property 'name' of null" at runtime if you are not using a type-checker.

After:

function find(id: number): Optional<{ name: string }> {
    return Optional.ofNullable(
        Math.random() * 10 < id
            ? null
            : { name: 'Test User' }
    );
}

find(5).ifPresent(u => console.log(u.name)); // This statement will never crash

// Also, if you want to manage the Empty case
find(5)
    .ifPresent(u => console.log(u.name))
    .ifEmpty(() => console.log('User not found'));

// Or, to be more concise
find(5)
    .if(u => console.log(u.name), () => console.log('User not found'));