Nim for TypeScript Programmers

Table Of Contents

Comparison	Variables	Ternary operators	Anonymous Functions
Arrow Functions	This	Server-Side Render	Client-Side Render
Svelte	Parcel	CommonJS	WebGL GUI
Electron	React	WebAssembly	Build Modes
Minification	Obfuscation	Compile-Time Function Execution	JavaScript Interoperability
Interoperability Template	Regular Expressions	Pragmas for Interoperability	HTML/CSS WYSYWIG Editor for Nim
Cheatsheet PDF	Run in NodeJS	BigInt

DISCLAIMER!

Unofficial, work in progress! This is still a stub. Please help extending it. There may be inaccuracies in this guide. The guide assumes some intermediate knowledge.

The general tutorials can be found here:
http://nim-lang.org/docs/tut1.html
http://nim-lang.org/docs/tut2.html

The manual provides an overview of the language: http://nim-lang.org/docs/manual.html

Comparison

Feature	TypeScript	Nim
Execution model	JavaScript code (Compiler)	JavaScript code (Compiler)
Written using	TypeScript	Nim
License	Apache	MIT
Version (Major)	3.x	1.x
Typing	Static, "provably correct" types	Static, Strong, Inferred
Meta-programming	❎ #issue-13252, Decorators are limited	✔️ template, macro
int8/16/32/64 types	❎	✔️
float32/float64 types	❎	✔️
Char types	❎	✔️
Subrange types	❎ #issue-225324972	✔️
JSON types	❎ #issue-56296923	✔️
Regex types	❎ #issue-128264906	✔️
Option types	❎	✔️
Dependent types	❎	✔️
Operator Overloading	❎	✔️
Custom Operators	❎	✔️
Run-time Checks	❎	✔️
Side Effects Tracking	❎	✔️
Enum types	✔️	✔️
Immutability	Limited, readonly keyword	✔️
Function Arguments Immutability	Mutable	Immutable
Full DOM API	✔️	✔️
console.log() anywhere	❓ Compiler complains	✔️
console.assert() anywhere	❓ Compiler complains	✔️
NodeJS integration	✔️	✔️
Generics	✔️	✔️
Type inference	✔️	✔️
Closures	✔️	✔️
Object-Oriented	✔️	✔️
Methods	✔️	✔️
Exceptions	✔️	✔️
Anonymous Functions	✔️	✔️
Arrow Functions	✔️	✔️
Array Comprehensions	✔️	✔️
Formatted String Literals	✔️	✔️
FFI	✔️ JS only	✔️ C/C++/JS
Async	✔️	✔️
Regex	✔️	✔️
Self-Documentation comments	✔️	✔️
Package Publishing	✔️	✔️
Package Manager	✔️	✔️
Code AutoFormatter	✔️ via NPM	✔️ Nimpretty
File extensions	.ts, .tsx	.nim, .nims

Variables

Creating a new variable uses var or let or const. Nim has immutability and compile-time function execution. You can assign functions to variables. const is different from TypeScript by being truly immutable.

Declaration	Compile-Time	Run-Time	Immutable	Requires Assignment	AutoInitialized
var	❎	✔️	❎	❎	✔️
let	❎	✔️	✔️	✔️	✔️
const	✔️	❎	✔️	✔️	✔️

If you are just starting from scratch, you can use var while learning, it will not produce an error for doing so, until you learn more.

Ternary operators

conditional ? "result0" : "result1"

⬆️ TypeScript ⬆️          ⬇️ Nim ⬇️

if conditional: "result0" else: "result1"

You probably notice that the Ternary Operator is just an if..else inline.

Anonymous Functions

var variable = ((var1: number, var2: number) => {
    return var1 + var2
})();

⬆️ TypeScript ⬆️          ⬇️ Nim ⬇️

var variable = (proc (var1, var2: int): int = var1 + var2)

Anonymous Functions in Nim are basically a function without a name and surrounded by parens.

This

this in Nim does not have a fixed or hardcoded naming, so you may see some code using self, Nim only cares about it being the first argument. this or self is immutable by default.

type Kitten = object
proc purr(this: Kitten) = echo "Purr Purr" # this
proc meow(self: Kitten) = echo "Meow Meow" # self

Arrow Functions

Nim has Arrow Functions, they are syntax sugar for normal functions. Using Arrow Functions requires import sugar.

Lets convert the Kitten example to use Arrow Functions.

import sugar
type Kitten = object
let purr = (this: Kitten) => echo "Purr Purr" # this
let meow = (self: Kitten) => echo "Meow Meow" # self

If you do not need to pass any argument, just do not pass anything.

import sugar
let purr = () => echo "Purr Purr" # No arguments

You can use function names with your Arrow Functions:

functionName(argument0, argument1: int) => argument0 + argument1
another_name(argument0, argument1: int) => argument0 + argument1

You can use Pragmas on your Arrow Functions:

let functionName = () {.inline.} => 42
let another_name = () {.inline.} => 42

You can use function names and Pragmas on your Arrow Functions:

function_name(argument0, argument1: int) {.noSideEffect.} => argument0 + argument1
let variab = (argument0, argument1: int) {.noSideEffect.} => argument0 + argument1

• Note that .then() and .catch() works for Async code.

Server-Side Render

Nim Source Code Filters NimF does server-side rendering of templates, a powerful templating engine on standard library.

Nim Source Code Filters use a header like a SheBang #?stdtmpl and the file extension *.nimf, then everything inside is just normal Nim code with the prefix #, they are usually functions that return a string, functions can use normal string operations and formatting, they get compiled into normal Nim code, providing excellent performance.

#?stdtmpl
#func generateXML(name, age: string): string =
<xml>
  <name> $name </name>
  <age>  $age  </age>
</xml>

Client-Side Render

Karax does Client-Side Render in Nim, it can do Server-Side render too, includes local dev server, among other really cool things.

Hello World, Client-Side

include karax/prelude
setRenderer (func(): auto = buildHtml(tdiv): text"Hello World")

Hello World, Server-Side:

import karax/[karaxdsl,vdom]
writeFile "app.html", $(block: buildHtml(tdiv):
  h1: text"Hello World"
  p: text"Compile:  nim r file.nim ")

• https://github.com/pragmagic/karax

Compile-Time Function Execution

Nim has Compile-Time Function Execution that allows you to run Backend-like code at compile-time and use it on Frontend at run-time. Compile-time FFI is also possible. Most code that works at compile-time and NimScript also tends to work for Frontend.

Example: Compile-time recursive file system walk module.

Svelte

Nim has some similarities with Svelte for Frontend, but at the time of writing Svelte does not fully supports TypeScript. You can think of Nim like a Svelte but with TypeScript like static typing and a whole Backend ecosystem. Svelte can not do Backend (is not designed to).

• Svelte inspired Nim Frontend https://mildred.github.io/nclearseam

Note: Svelte added TypeScript

Parcel

Theres a Nim module for ParcelJS support:

https://github.com/nepeckman/parcel-plugin-nim#parcel-plugin-nim

CommonJS

Theres a Nim module for CommonJS support:

https://github.com/nepeckman/jsExport.nim#jsexportnim

WebGL GUI

Cross-platform GUI framework with WebGL target, compiles your GUI to WebGL:

https://github.com/yglukhov/nimx#nimx--

Electron

You can run Nim inside Electron.

You can also use cross-platform tiny (1 .h file) and fast (C code) WebView:

• https://github.com/juancarlospaco/webgui#buit-in-dark-mode
• https://github.com/oskca/webview#webview-for-nim

WIISH also provides a similar cross-platform WebView, with other targets too: https://github.com/iffy/wiish#features

If it is not mandatory to be a JavaScript-only GUI, and you just need a GUI that works on Windows/Linux/Mac, then you have even more alternatives to try:

• https://github.com/yglukhov/nimx#nimx--
• https://github.com/filcuc/nimqml#nimqml
• https://github.com/ba0f3/uibuilder.nim#uibuildernim
• https://github.com/khchen/wNim#wnim
• https://github.com/trustable-code/NiGui#nigui
• https://github.com/johnnovak/illwill#main-features
• https://github.com/stefansalewski/gintro
• https://github.com/nim-lang/ui#ui
• https://github.com/zacharycarter/nimgui#nimgui

React

ReactJS for Nim:

https://github.com/andreaferretti/react.nim#reactnim

WebAssembly

You can compile your Nim code to WebAssembly using:

• Clang WASM target OR Emscripten OR NLVM.

For compiling your project to WebAssembly see:

• https://github.com/def-/nimes#nimes-nes-emulator-in-nim-
• https://github.com/arnetheduck/nlvm#introduction
• https://github.com/2vg/nim-wasm-example
• https://github.com/yglukhov/nimwasmrt#wasmrt-

Build Modes

When your code is ready for production you should use a Release build, you can add to the compile command -d:release -d:danger.

Feature	Release Build	Debug Build
Speed	Fast	Slow
File Size	Small	Big
Optimized	✔️	❎
Tracebacks	❎	✔️
Run-time checks	✔️	✔️
Compile-time checks	✔️	✔️
assert	❎	✔️
doAssert	✔️	✔️

Minification

Nim does not Minify the compiled JavaScript by default.

Nim typically compiles to very small file sizes when builds for release, thanks to Dead Code Elimination only the used symbols of each Nim module gets compiled and is present on the output file, if you import a module and is unused it will not exist on the output file (and a Hint shows on the terminal about unused import).

Nim uses spaces as indentation. Basically you are good to go with the JavaScript file that Nim compiles.

Alternatively you can use any other minifier software to do that kind of post-processing of JavaScript.

Obfuscation

Nim does not obfuscate the compiled JavaScript by default.

If you want to obfuscate the compiled JavaScript, you can control the name mangling, among other more useful features using {.exportc.} pragma, to use the mangling as obfuscator.

var variable {.exportc: "lkfnjmgkw3du4905r3q2ep8n4urfp34w2efltgvepotik132qm0".} = false
proc funct() {.exportc: "kl34jgo9liw35e4atr8i30q2rk1fipkpfrsdofir93o2qujfoks".} = echo 42

Compiles to:

var lkfnjmgkw3du4905r3q2ep8n4urfp34w2efltgvepotik132qm0 = false;

function kl34jgo9liw35e4atr8i30q2rk1fipkpfrsdofir93o2qujfoks() {
  rawEcho("42");
}

You use the human friendly names variable and funct, while the code compiles to the obfuscated names.

Nim will not lose track of the names, you can generate the obfuscated names with any random algo of your own.

Alternatively you can use any other obfuscator software to do that kind of post-processing of JavaScript.

JavaScript Interoperability

Nim can directly interoperate with JavaScript, here is how you can create your own libs.

There is no additional performance cost, the compiler will just emit the code you want.

As minimal as possible example, not too useful but explains as simple as possible:

func functionName(argument: SomeNumber) {.importjs: """ console.log(#) """.}

• # is replaced by arguments by index, starting at index 0, if any.
• @ is replaced by all remaining arguments, if any, separated by comma.
• $$ to escape a single $ on string or Regex.
• $1 is replaced by the current function name.
• Argument types and return types are Nim types, from std lib or your own custom.
• importcpp is sometimes used as importjs.
• You can use openArray as return type on functions, it will return array instead of seq.
• Print to console using vanilla JavaScript console.log() and similar.
• Ensure that DOM is ready using vanilla JavaScript (function(){ ... })();.
• Enforce Strict Mode using vanilla JavaScript "use strict";.
• https://nim-lang.org/docs/manual.html#implementation-specific-pragmas-importjs-pragma
• If the function has no arguments, then @ generates nothing (empty).
• If the function has no arguments, then # produces an error.
• Note that with @ commas are automatically inserted, with # you must add the commas.
• You can use multi-line strings for the patterns.
• You can use strformat for the patterns, but you must import strformat.

Lets compile this tiny example to JavaScript target:

func functionName(argument0, argument1: SomeNumber) {.importjs: """ console.log(#, #) """.}

functionName(42, 9)

⬆️ Nim ⬆️          ⬇️ JavaScript ⬇️

console.log(42, 9);

If you need to use named arguments you can use {.emit.} pragma:

func functionName(namedArgument: int) = {.emit: """ console.log( `namedArgument` ); """.}

• `namedArgument` is replaced by arguments by name.
• Argument types and return types are Nim types, from std lib or your own custom.
• Print to console using console.log() and similar.
• You can use openArray as return type on functions, it will return array instead of seq.
• Ensure that DOM is ready using vanilla JavaScript (function(){ ... })();.
• You can use "use strict" if you want, but it may not have effect.
• The rest is similar to importjs, as explained above.
• https://nim-lang.org/docs/manual.html#implementation-specific-pragmas-emit-pragma

Lets compile this tiny example to JavaScript target:

func functionName(namedArgument, otherArgument: int) = {.emit: """
  console.log( `namedArgument`, `otherArgument` );
""".}

functionName(42, 99)

⬆️ Nim ⬆️          ⬇️ JavaScript ⬇️

function function_name(named_argument, other_argument) {
  console.log( named_argument, other_argument );
}

function_name(42, 99);

More Examples:

func example0(argument0, argument1, argument2: SomeNumber | string) {.importjs: """
(function () {
  "use strict";
  console.log('Argument0 = ' + #, 'Argument1 = ' + #, 'Argument2 = ' + #);
})(); """.}

func example1(foo, bar, baz: SomeNumber) = {.emit: """
  console.log('foo = ' + `foo`, 'bar = ' + `bar`, 'baz = ' + `baz`);
""".}

Useful Pragmas for Interoperability

• {.importjs.} import JavaScript.
• {.compiletime.} Force code to run at compile-time.
• {.exportc.} Escape Name Mangling (for Debug, Obfuscation, etc).
• {.emit.} Emit code directly with passed arguments.
• {.varargs.} Force a function to accept several arguments.
• {.hint.} Human-friendly colored messages at compile-time that generates no code.
• {.warning.} Human-friendly colored messages at compile-time that generates no code.
• {.codegendecl.} Emit code directly on code generator.
• {.noinit.} Escape implicit variable auto-initialization.
• {.discardable.} Allow to discard unused return values (for debug, quick prototyping, etc).
• {.noreturn.} Force a function to never return
• {.asmnostackframe.} Force a function to not have the result = auto-injected, useful with {.emit.}
• {.injectStmt.} Inject code before every other statement in the current module.
• Pragmas are just macro, so you can create your own.

See also:

• static: / static() Force a block of code to run at compile-time.
• when Compile-time if
• jsre module for an example of actual code.
• jsconsole module for an example of actual code.

Interoperability Template

• Nim "code template" pseudocode that you can Edit to create your own JavaScript libs:

func functionName(argument: SomeNumber | string | bool): SomeNumber {.importjs: """
(function () {
  "use strict";

  console.log("CODE HERE");
  console.log(#);
  return 42;

})(); """, exportc: "functionName".}  ## Documentation Comment.


func functionName2(namedArgument: SomeNumber | string | bool): SomeNumber = {.emit: """

  console.log("CODE HERE");
  console.log( `namedArgument` );
  return 42;

""", exportc: "functionName2".}  ## Documentation Comment.

HTML/CSS WYSYWIG Editor for Nim

This is a community maintained open source project thats a HTML/CSS WYSYWIG Editor with Nim Support without JavaScript required, for creating Source Code Filter starter templates (similar to Pug templating, etc), so you dont have to start by hand with an empty blank file, not meant to produce a "finished" page but a template to edit. Ideas to make it more useful welcome. Pull Requests welcome.

• Drag&drop your components in the page and press the "View Code" green button.
• Documentation of each component clicking on the "?" link.
• Ready-made full-page templates on the "Templates" category.

Spectre CSS

Uses Spectre CSS because it wont need third-party JavaScript libraries, is 9 Kilobytes, pure CSS, JavaScript framework agnostic.

• https://juancarlospaco.github.io/grapespectre

Bulma CSS

Uses Bulma CSS because it wont need third-party JavaScript libraries, pure CSS, JavaScript framework agnostic.

• https://juancarlospaco.github.io/grabulma

NodeJS Compatibility

• NodeJS Standard Library for Nim

More

To not duplicate all documentation here, please continue reading:

• https://github.com/nim-lang/Nim/wiki/Nim-for-Python-Programmers#table-of-contents

It is Python-oriented, but the same concepts also work for Frontend too!.

⬆️ ⬆️ ⬆️ ⬆️