README.md

SkertJS

JavaScript-to-JavaScript compiler tools for holistic language design.

• About
• Features
• Install
• CLI
• API
• Online REPL

About

SkertJS reimagines the future of JavaScript with simple features that address common problems and work well together.

Features

Top-Level Await

Top-level await allows the programmer to use use await expressions from the top level of a module body.

let response = await fetch(url);
let text = await response.text();
console.log(text);

NOTE: Currently, top-level await is not supported in modules with export declarations.

Call-With Operator

The call-with binary operator (->) allows the programmer to call a function as if it were a method.

function sayHello(obj, timeOfDay) {
  console.log(`Good ${ timeOfDay }, I'm ${ obj.name }.`);
}

let me = { name: '@zenparsing' };

me->sayHello('morning'); // "Good morning, I'm @zenparsing."

Method Extraction Operator

The method extraction prefix operator (&) allows the programmer to extract a method from an object. The extracted method is bound to the object.

let me = {
  name: '@zenparsing',
  hello() { return `Hello, I'm ${ this.name }.`; }
};

let hello = &me.hello;

console.log(hello); // "Hello, I'm @zenparsing."

// Method extraction is idempotent
console.log(hello === &me.hello); // true

Null Coalescing Operator

The null coalescing binary operator (??) allows the programmer to specify a default value when applied to null or undefined.

let obj = { x: 0, y: null };

console.log(obj.x ?? 1); // 0
console.log(obj.y ?? 1); // 1
console.log(obj.z ?? 1); // 1

Symbol Names

Symbol names allow the programmer to effectively use symbols that are local to a module or script.

let obj = {
  @foo: 1
};

console.log(obj.@foo); // 1
console.log(Reflect.ownKeys(obj)); // [Symbol('@foo')]

Build-Time Macros

Macros give the user the ability to transform the program structure at build-time.

import { deprecated } from './macros/deprecated.js';

#[deprecated]
function dontUseMeAnymore() {
  eval('You wrote a bad song Petey!');
}

import { templates } from 'ast-helpers';

export function deprecated(ast) {
  ast.body.statements.unshift(templates.statement`
    console.warn('This function is deprecated');
  `);
  return ast;
}

Class Mixins

Class mixins allow the programmer to copy additional methods from another class.

class A {
  a() { return 'a' }
}

class B {
  b() { return 'b' }
}

class C with A, B {}

const c = new C();

c.a(); // 'a'
c.b(); // 'b'

Class Initializer Blocks

Class initializer blocks allow the programmer to execute code when a class is defined.

class Widget extends HTMLElement {
  static {
    window.customElements.define('acme-widget', this);
  }
}

Install

npm install @zenparsing/skert

CLI

skertc [input_path] ...options

Options

• --output [output_path], -o [output_path]: Specifies the output file or directory
• --script: Parse the input file or files as scripts instead of modules
• --cjs: Output CommonJS-formatted modules
• --sourcemaps, -s: Output source maps

API

compile(code, options = {})

Compiles the specified input string and returns a CompileResult object.

Options

• module (boolean): If true, the input is parsed as a module instead of a script.
• transformModules (boolean): If true, modules are translated into CommonJS format.
• context (Map): A map containing state which can be persisted between calls.
• location (string): The path associated with code.
• sourceMap (boolean | 'inline'): If, true a source map will be generated and attached to the result object. If 'inline', the source map will be added to the output code.

Example

import { compile } from '@zenparsing/skert';

let result = compile('export const x = 1;', {
  module: true,
});

console.log(result.output);

CompileResult

Properties

• output (string): The compiled output
• mappings (Array): A list of input-to-output source code mappings
• sourceMap (null | JSON): A source map JSON object
• context (Map): A Map representing compiler state