Scope Functions

Porting the scope functions from the Kotlin standard library to JavaScript/TypeScript

Installation

npm i scope-funs

API

Scope creation

import { scope } from 'scope-funs'

const scopeValue = scope([1])

// or

import { Scope } from 'scope-funs'

const scopeValue = new Scope([1])

Methods

Method	Description
let	Invoke one or more functions on results of call chains
also	Performing some actions that take the context object as an argument
takeIf	Returns self if predicate is true, otherwise undefined
takeUnless	Returns self if predicate is false, otherwise undefined
skipNullish	Returns self for non-nullish values, otherwise undefined
unwrap	Extracts the underlying value from the Scope

The skipNullish and unwrap methods do not exist in the Kotlin. These are additional methods that are needed because JavaScript does not have the extension function feature and the library uses a wrapper around values

In the Kotlin, we can call scope function on any value. As example:

val str: String? = "Hello"

val length = str?.let {
    println("let() called on $it")
    it.length
}?.let { it + 1 }

The equivalent of this code would be:

import { scope } from 'scope-funs'

const str: string | undefined = 'Hello'

const length = scope(str)
  .skipNullish()
  ?.let((it) => {
    console.log(`let() called on ${it}`)
    return it.length
  })
  .let((it) => it + 1)
  .unwrap()

Usage

Basic

import { scope } from 'scope-funs'

const result = scope(5)
  .let((it) => [it]) // Transforms the value
  .also((it) => {
    console.log(`Current value: ${it}`)
    it.push(10)
  }) // Some action
  .unwrap()
// Prints "Current value: 5" and returns [5, 10]

Conditional Operations

import { scope } from 'scope-funs'

const positiveScope = scope(-5).takeIf((it) => it > 0) // Returns undefined
const negativeScope = scope(-5).takeUnless((it) => it > 0) // Returns the Scope instance

Nullish Handling

import { scope } from 'scope-funs'

const value: string | null = null

const result = scope(value)
  .skipNullish()
  ?.let((it) => it.length) // it is not nullish
  .unwrap() // Returns the length of the value if it is not nullish or returns undefined

// or

const resultNullish = scope(value)
  .let((it) => it?.length ?? 0) // it is nullish
  .unwrap() // Returns the length of the value if it is not nullish or 0