scope-extensions-js

Package for using Kotlin's Scope Function Extensions on JavaScript and TypeScript.

It also supports the use of the new Optional Chaining Operator, bringing the logic of Kotlin's Null Safe Calls to the JavaScript world.

Installation

Just install the package using NPM

npm i --save @starrah/scope-extensions-js

and import it directly to any file.

// normal version (`use()` and `.item()`)
const use = require("@starrah/scope-extensions-js").use;
// prototype injection version (use with caution)
require("@starrah/scope-extensions-js/prototype")

You can also use ES6 syntax.

// normal version (`use()` and `.item()`)
import use from "@starrah/scope-extensions-js";
// prototype injection version (use with caution)
import "@starrah/scope-extensions-js/prototype";

For browser, reference directly to node_modules path

<!-- normal version (`use()` and `.item()`) -->
<script src="node_modules/@starrah/scope-extensions-js/dist/index.js"></script>
<!-- prototype injection version (use with caution) -->
<script src="node_modules/@starrah/scope-extensions-js/dist/prototype.js"></script>

or use it without installation by CDNs (unpkg/jsdelivr).

<!-- normal version (`use()` and `.item()`) -->
<script src="https://unpkg.com/@starrah/scope-extensions-js@2"></script>
<!-- prototype injection version (use with caution) -->
<script src="https://unpkg.com/@starrah/scope-extensions-js@2/dist/prototype.js"></script>

<!-- normal version (`use()` and `.item()`) -->
<script src="https://cdn.jsdelivr.net/npm/@starrah/scope-extensions-js@2"></script>
<!-- prototype injection version (use with caution) -->
<script src="https://cdn.jsdelivr.net/npm/@starrah/scope-extensions-js@2/dist/prototype.js"></script>

Note that the type="module" tag is not needed.

Usage

Wrap your value with use() function, which returns a Wrapper that wraps your value when it is not undefined.
When your value as the argument of use() is undefined, use() will return undefined.

Then on the Wrapper, you can use functions let, also, run or apply and it'll be passed as the argument or the context of a scope function.
The return value of the scope functions is still a Wrapper or undefined.

Finally, you can use Wrapper.item() to retrieve the value from the Wrapper.

import use from "@starrah/scope-extensions-js";

const obj = { name: "Daniel", age: 30 };

use(obj).let(it => {
    return it.age < 0 ? it.age : 0;
}).also(it => {
    console.log(it);
}); // prints 30

const obj2Wrapper = use(obj).let(it => {
    return it.age < 0 ? it.age : 0;
}).item() // obj2 is of type number

This way, you can execute a block of code only if a value is neither null nor undefined.

import use from "@starrah/scope-extensions-js";

const str: string | null = await getData();

// later
use(str)?.also(it => {
    console.log(`Already initialized: ${it}`);
}) ?? console.log("Still not initialized");

The above code is equivalent to this

if (str != null && str != undefined)
    console.log(`Already initialized: ${str!}`);
else
    console.log("Still not initialized");

The usage of takeIf & takeUnless is a bit different. You can call any value with takeIf and it will return the caller instance if the predicate is true, or undefined if it's false (and vice versa when using takeUnless).

import use from "@starrah/scope-extensions-js";

const account = await getCurrent();

use(account).takeIf(it => {
    return list.includes(it.id);
})?.also(it => {
    console.log(it);
}) ?? console.log("Not included");

Usage (By Prototype Injection)

Use with caution!

Import this file will add {let, also, run, apply} on the prototype of built-in type Object, String, Number and Boolean, which means you can easily use x?.let(...) without wrap x with use(x), even when x is not an object (e.g. x is a number). However, modify the prototype of built-in types like Object may cause compatibility issues with other packages, if they read or modify the properties we add on the prototype. So please use this file with caution! If you see wired behaviours on other codes, please do not use this file. Instead, you should only require(@starrah/scope-extensions-js) and always use use(x)?.let(...).item().

Simply call any value with let, also, run or apply and it'll be passed as the argument or the context of a scope function.

const obj = { name: "Daniel", age: 30 };

obj.let(it => {
    return it.age < 0 ? it.age : 0;
}).also(it => {
    console.log(it);
}); // prints 30

This way, you can execute a block of code only if a value is neither null nor undefined.

const str: string | null = await getData();

// later
str?.also(it => {
    console.log(`Already initialized: ${it}`);
}) ?? console.log("Still not initialized");

The above code is equivalent to this

if (str != null && str != undefined)
    console.log(`Already initialized: ${str!}`);
else
    console.log("Still not initialized");

The usage of takeIf & takeUnless is a bit different. You can call any value with takeIf and it will return the caller instance if the predicate is true, or undefined if it's false (and vice versa when using takeUnless).

const account = await getCurrent();

account.takeIf(it => {
    return list.includes(it.id);
})?.also(it => {
    console.log(it);
}) ?? console.log("Not included");

Differences

We could group the 4 main extensions into 2 groups of 2 each, based on both the argument type and the return value:

• let & also receive the caller instance as a function parameter, and run & apply receive the caller instance as the function context (this).
• let & run return the function result (return) value, and also & apply return the caller instance (this).

Summed up in this table:

Note that let & also can be called with standard lambda/arrow functions, but because JavaScript arrow functions don't have an own this context, run & apply have to be called with standard functions.

Here is an example of each one of them:

• let

const data: Array<number> | null = await idsFromFile();

const str = data?.let(it => 
    processToString(it);
) ?? "empty";

• also

const list: Array<string> = model.getNames();

const filtered = list.also(it => 
    it.slice(0, 4);
).also(it =>
    applyFilter(filter, it);
).also(console.log);

// same as
const filtered = list.also(it => {
    it.slice(0, 4);
    applyFilter(filter, it);
    console.log(it);
});

• run

const list: Array<object> | undefined = currentAcc?.getContacts();

const lastsByName = list?.run(function() {
    this.filter();
    this.reverse();
    return this.slice(0, 3);
});

• apply

const obj = { name: "Daniel", age: 30 };

obj.apply(function() {
    this.name = "Dan";
    this.age++;
    this["country"] = "Canada";
});

License

Copyright © 2020 TheDavidDelta.
This project is MIT licensed.