Option

Rust-like Option for TypeScript

npm i @hazae41/option

Node Package 📦

Features

Current features

• 100% TypeScript and ESM
• No external dependencies
• Similar to Rust
• unwrap() for throwing
• unwrapOr() for default value
• map() for mapping (sync/async)
• isSome()/isNone() type guards
• ok()/okOr() for converting to Result from @hazae41/result

Why

TLDR undefined is too low level and often leads to ugly and repetitive design patterns or bugs

When designing a function, you often encounter the case where you can't pass undefined.

function doSomething(text: string) {
  return Buffer.from(text, "utf8").toString("base64")
}

function bigFunction(text?: string) {
  // ...

  doSomething(text) // what if text is undefined?

  // ...
}

So you end up checking for undefined

Checking in the caller

function bigFunction(text?: string) {
  // ...

  if (text !== undefined) {
    doSomething(text)
  }
  
  // ...
}

This is annoying if we want to get the returned value

function bigFunction(text?: string) {
  // ...
  
  if (text !== undefined) {
    const text2 = doSomething(text)
  }

  // can't use text2
}

Checks become redundant if you need to map the value or throw an error

function bigFunction(text?: string) {
  // ...
  
  const text2 = text === undefined
    ? undefined
    : doSomething(text)

  // ...

  const text3 = text2 === undefined
    ? undefined
    : doSomethingElse(text2)

  // ...

  if (text3 === undefined) 
    throw new Error(`something is wrong`)
  
  // use text3
}

Checking in the callee

Why not check for undefined in the callee then?

function maybeDoSomething(text?: string) {
  if (text === undefined) return

  return Buffer.from(text, "utf8").toString("base64")
}

If you know your argument is NOT undefined, it will force you to check for undefined after the call

function bigFunction(text: string) {
  // ...
  
  const text2 = doSomething(text) // text is never undefined

  // text2 can now be undefined
}

Or even worse, force you to use type assertion

function bigFunction(text: string) {
  // ...
  
  const text2 = doSomething(text) as string

  // ...
}

Checking in an intermediary

Let's keep the original function and create an intermediary function for undefined

function maybeDoSomething(text?: string) {
  if (text === undefined) return

  return doSomething(text)
}

Now you have twice the amount of function in your app, and if one of them changes you have to change its intermediary function too

Using Option

function bigFunction(text?: string) {
  const maybeText = Option.from(text)

  // ...
  
  // you want to map it?
  const maybeText2 = maybeText.mapSync(doSomething)

  // ...

  // you want to map it again?
  const maybeText3 = maybeText2.mapSync(doSomethingElse)

  // ...

  // you want to quickly throw an error?
  const text4 = maybeText3.unwrap() // string

  // you want to throw a custom error?
  const text4 = maybeText3.okOr(new Error(`Something is wrong`)).unwrap()

  // you want to get a result?
  const text4 = maybeText3.ok() // Result<string, Error>

  // you want to get a custom result?
  const text4 = maybeText3.okOr(new Error(`Something is wrong`))
  
  // you want to come back to "string | undefined"?
  const text4 = maybeText3.inner // string | undefined

  // you want to do manual check?
  if (maybeText3.isSome())
    const text4 = maybeText3.inner // string
  else
    // ...
}