# Javascript | Typescript


javascript is a language that people love to hate

most of the backend stuff is abstracted using technological solutions like

  • cloud platforms AWS, GCP
  • docker
  • APIs like stripe/paypal for payment

Typescript is both, a type checker and a transpiler

~ Anonymous

# History

  • came to be in 1995
  • Wasnt designed to be fast, its hard to make it fast.
    • Dynamic types
      • compiler dont know if a variable would be integer or a strings
      • could even change at runtime
  • 2008 browser wars

Programming is like talking to aliens

~ Lin Clark
  • Why do we even need webassembly, isnt javascript enough?
  • How is modern javascritp made faster?
  • How modern javascipt getting better?

Compiler is human to alient translator

  • we would need a whole bunch pf translators to translate any given language to x86 assembly
    • pretty insifficient
    • we take one layer in between called IR

# Stages in processing

  1. Parsing
  2. Compiling
  3. optimising
  4. re-optimizing
  5. executing the code
  6. Garbage collection

# Backgroubd

  • Up until 2015 javascript did not had modules as like in other languages (ES6)
    • We need to export const, var, let, functions, classes from module files to use it as a package
    • single export { ... } is preferred over multiple exports for redability
    • Then import javascript objects in source to use them from modules.
    • How do we pack everything up from all modules?
  • Build Toolchain
    • compilers - node
    • transpilers - babel
      • to use lates ES features which are not yet supported by browsers
    • bundlers - combine all modules taking care of dependencies and order of appearence
      • your code + code from npm + posssibly other sources
      • IFE (Immediately Invoked Function Expression)

So where is the majority of development?

What got you interested? Why research it?


Vue3 totally re-written in typescript

vue3 next repo on github code breakdown

What C++ is to C is the same for what Typescript is to Javascript

  • It is a superset of Javascript

Let see an important landmark in the history of Javascript:

It was launched in September 1995, and It took just ten days to develop this e scripting language which was initially called Mocha In November 1996, Netscape submitted JavaScript to ECMA (European Computer Manufacturers Association) International ECMAScript 2 was released in 1998 ECMAScript 3 was released in 1999 In 2005, Eich and Mozilla join ECMA to develop E4X Java script In January 2009, the CommonJS project was launched with the aim of defining a common standard library In June 2011, ECMAScript 5.1 was released In June 2015. ECMAScript 2016 was released The current version is ECMAScript 2017 which was released in June 2017

Javascript vs Typescript google trends results for last 5 years

  • Programming Languague maintained by Microsoft
  • Adds static type checking to javascript
  • Typescript code needs to be compiled
  • As TypeScript is a superset of JavaScript, existing JavaScript programs are also valid TypeScript programs.
  • The TypeScript compiler is itself written in TypeScript and compiled to JavaScript.

TypeScript is a strict superset of ECMAScript 2015, which is itself a superset of ECMAScript 5, commonly referred to as JavaScript.

The TypeScript compiler, named tsc, is written in TypeScript.

s a result, it can be compiled into regular JavaScript and can then be executed in any JavaScript engine (e.g. a browser). The compiler package comes bundled with a script host that can execute the compiler. It is also available as a Node.js package that uses Node.js as a host.

Would you rather have silly errors during development or insanity induced error in production!

  • Learn it incrementally as you go
  • transpile to it multiple javascript flavours
  • try writing async await in TypeScript
  • By default tsc transpiles to ES3 syntax
  • tsconfig.json file for compiler options
    • target ES syntax
    • watch the files?
    • lib -include native dom classes in your applications
      • get free vscode autocomplete and intellisense
  • Programming Languagues
  • Meaning of <T>
    • Type variable
    • better than arg: any
public void foo() {
    int x = 5;
    boolean b = x;

def erroneous():
    s = 'cat' - 1


tsc hello.ts -> hello.js // vanilla

Remove type checcking for a variable

let lucky: any = 23;
lucky = '23'

Pascal Case

  • Restrictign the value of variable to certain values |
  • Create type interfaces for structs
  • String typing a function
    • argumsnt annotation
    • return types
function pow(x: number, y: number): string {
  return Math.pow(x, y).toString();

// Arrays, Tuples
// make them optional
type MyList = [number?, string?, boolean?]

class Observable<T> {
  constructor(public value: T) {}

# Debug like a pro

  • computed property nams, adding variables to object
    • console.log({foo, bar, baz})
  • Add custom CSS styles to logs
  • Display objects as tables
  • console.trace()
    • where was fucntion defined and where was it called?
  • Object Destructuring
  • Template Literals
  • Spread Syntax
  • A comma in the end would not break modern JS
  • Modern Arrays
    • array reduce
    • array map
    • array filter
  • Async await
    • express asynchronous code in synchronous format
    • one of the best things that has ever happened to JS
console.log('%c My Friends', 'color: orange;')
console.log([foo, bar, baz])

// Equivalent of array push
pokemon = [...pokemon, 'Balbasaur']
// convert array to object
let data = this.$store.state.cart.map(item => ({ [item.productId] : item:productQuantity }))
data = Object.assign({}, ...data)

# Type conversion

string -> json Object -> Array Object -> Array

# Advanced typescript

  • Advanced types
  • Intersection Types
  • Template literals (Template strings) using backticks ```
type Duck = Quackable & Swimmable;
type Flyable = Eagle | Butterfly;

# 🔧 Bundler Softwares for Frontend

  1. webpack
  2. Rollup
Universal Module Definition - UMD

UMD is a pattern of universal module definition for JavaScript modules.

These modules are capable of working everywhere, be it in the client, on the server or elsewhere.

# Why do we need webpack?

Generic way of consuming JS on on webpage

  • Script tags
    • jQuery repreccursions
  • Put everything into one BIG JS file
    • scoping
    • maintenance
  • Modules
  • ESM
javascript bundler. Creates bundles
By default, webpack deals only with JS files, but we might need other assets as well like images, vue files, css, html templates files, preprocessing, postprocessing etc
do fancy stuff with loaded files. Vuetify etc

# Rollup

Another build tool similar to webpack, grunt, browserfy

  • Bundles only the packages which are actually used in source, unlike webpack which bundles everything together
  • results in small final source bundle
  • built for ES6
  • compiler a JS

# Functional Programmming


# Webpack Bundler

Asset bundler, minified js

  • Out of the box, webpack only understands JavaScript and JSON files.
  • Adds all dependencies to final output file
  • Transpiling with babel - writing modern JS
  • Tree shaking - elimination of dead code
  • webpack by default will look for a src folder with index.js file to dist/index.js
  • if we use HtmlWebpackPlugin webpack will auto add index.js to html
  • MiniCssExtractPlugin same thing for css, compiler sass css preprocessor etc
  • Loaders teaches webpack how to deal with all sorts of file
    • svg-inline-loader, pug loader, remark markdown loader
    • css-loader : turns css to javascript
    • style-loader : takes javscript and applies it as CSS style

# Questions

  • How to create javascript binaries?

# Function Calls

  1. Function executuon wheen called
  2. Self executing functions, without calls. Gets executes as soon as they appearence
var myFunc1 = function() {
}();                        // <--- () causes self execution

var myFunc2 = function() {
    return 5 + 5;

var some_value = myFunc2(); // <--- Again () causes execution (you'd expect this one)

# References