Advanced Typescript

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Category:JavaScript


title
Advanced Typescript Training Course
author
Łukasz Sokołowski


Advanced Typescript

Advanced Typescript Training Materials

Introduction

  • Overview of TypeScript features and advantages
  • Programming best practices and tips
    • We'll cover some of them during the day

Getting Started

  • Installing TypeScript, Nodejs, and Visual Studio Code
  • Initializing the server
  • Configuring access modifiers and compiler options
  • Setting up a Node.js project
  • Building and debugging Node.js TypeScript

Configuring access modifiers and compiler options

  • Example with Angular - jwt
  • Related docs - aka.ms/tsconfig.json

Setting up a Node.js project

  • Example - other_/node_/

Configuring Webpack and TypeScript

  • Enabling source maps
  • Using third-party libraries
  • Importing non-code assets
  • Building the application

Initial setup

  • Exercise - webpack_/with_ts
  • Compiler and loader
    • npm install --save-dev typescript ts-loader
  • Directories and configuration
    • index.ts - new file with content from 'index.js' and change first line: import * as _ from 'lodash';
    • tsconfig.json - 'tsc --init' and later apply these changes
      {
  "compilerOptions": {
    "outDir": "./dist/",
    "noImplicitAny": true,
    "module": "es6",
    "target": "es5",
    "jsx": "react",
    "allowJs": true,
    "moduleResolution": "node"
  }
}
    • webpack.config.js
      const path = require('path');

module.exports = {
  entry: './src/index.ts',
  module: {
    rules: [
      {
        test: /\.tsx?$/,
        use: 'ts-loader',
        exclude: /node_modules/,
      },
    ],
  },
  resolve: {
    extensions: ['.tsx', '.ts', '.js'],
  },
  output: {
    filename: 'main.js',
    path: path.resolve(__dirname, 'dist'),
  },
};

Enabling source maps

  • Exercise - webpack_/with_ts
  • TypeScript will output inline source maps to our compiled JavaScript files
  • tsconfig.json - uncomment line with "sourceMap": true,
  • Telling webpack to extract source maps and include in final bundle
    • webpack.config.js - put this just below entry: devtool: 'inline-source-map',

Using third-party libraries

  • When installing new lib from npm
    • Always remember to install it's typing definition (.d.ts files)
    • Definitions can be found here Types for TS
  • Example - npm install --save-dev @types/lodash
  • Exercise - install jquery with it's typings
    • when we click on our div it should shout with popup: "TS rulezzzzz!"

Importing non-code assets

  • We need to defer the type
    • custom.d.ts - new file
    • example setup for .svg
      declare module '*.svg' {
  const content: any;
  export default content;
}
  • Same concept applies to other assets - CSS, SCSS, JSON, etc
  • Exercise - setup for .jpg and add bear.jpg in our div
    • webpack.config.js - add this to rules array
            {
        test: /\.(png|svg|jpg|jpeg|gif)$/i,
        type: 'asset/resource',
      },
    • index.ts - new image element
          //// at the top
    import MyBear from './bear.jpg';
    (...)
    //// in 'component()' function
    // Add the image to our existing div
    const myIcon = new Image();
    myIcon.src = MyBear;

    element.appendChild(myIcon);

Building the application

Creating Custom Data Types

  • Union, Intersection, and Tuple Types
  • Type Guards, Type Casting, and Type Assertions
  • Creating arrays for custom types
  • Other types and examples

Custom Data Types

  • Usually a combination of primitive types (strings, numbers, Booleans) with objects
  • Building blocks of advanced types – type alias, string, and number literals
  • Allow to write code
    • easier to understand for myself and easier to work with
    • and for any others working with me
    • or those who are inheriting the project
  • Oftenly web applications become more complex
    • it is necessary to be able to model that complexity
    • TypeScript makes that easy with advanced types
    • types that are conditional and flexible

Type Aliases

  • Allow to declare references to any type – advanced or primitive
  • Make code easier to read - allow to be less verbose
  • We declare our type once and reuse it throughout application
  • Code is more readable and maintainable
  • Syntax: type OnlyStrings = string;
    • The type keyword is followed by the alias, OnlyStrings, and then the string type
  • Exercise - customdt_/exerc_/ex1

Type Literals

  • Allow to create a type based on a specific string or number
  • Not very useful in itself, but with more complex types such as union types
  • Syntax: type Success = 200;
  • Example - customdt_/examp_/e2
  • Exercise - customdt_/exerc_/ex2

Intersection

  • Allows to combine types to form a new type
    • with the properties of the combined types
    • it is an and type
  • Similar to multi-class inheritance
    • child object can have more than one parent object that it derives its properties from
  • Helps to keep the cod DRY (Don't Repeat Yourself)
  • Merged properties should be of the same type
  • Syntax: type CourseEvaluation = TrainingEvaluationForm & CourseEventEvaluationByTrainer;
  • Example - customdt_/examp_/e3
  • Exercise - customdt_/exerc_/ex3

Union

  • Similar to intersection
    • but it is an or type
    • do not merges types
  • Similar to the ternary operator in JavaScript
    • types are separated by the | (pipe)
  • Syntax: type Lead = General | Price | Course;
  • Example - customdt_/examp_/e4
  • Exercise - customdt_/exerc_/ex4

Index Types

  • Allow to create objects with flexible number of properties
    • We define a signature for our type using an interface
  • Syntax: [ msg: number ]: string;
  • Example - customdt_/examp_/e5
  • Exercise - customdt_/exerc_/ex5

Tuple

  • Array which contains multiple types
    • fixed indexed order - the order and length are guaranteed
    • data is connected with less syntax than keyed objects
  • A good pattern for short bits of connected data or for fixtures
  • Example from 'Reactjs' - useState returns a tuple of the value and a setter function
  • Syntax: const closedLead: [Invoice, Payment] = ["Consultancy23032021", {paid:1, paymentType:"transfer"} ];
  • Example - customdt_/examp_/e6
  • Exercise - customdt_/exerc_/ex6

Type Guards

  • Participate in the code flow analysis
    • We influence the code flow
  • TS uses existing JS behavior which validates our objects at runtime
  • We can prep also custom functions - type predicate functions
  • Syntax/operators - in, instanceof, typeof, is
    • Full list of possible typeof values developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof
  • Example - customdt_/examp_/e7
  • Exercise - customdt_/exerc_/ex7

Type Casting, Assertions

Two syntaxes

Generics

  • Generics basics
  • Example - customdt_/examp_/e8_
  • Exercise - together with 'Conditional Types'

Conditional Types

  • Allow complex type expressions
    • drive some of the built-in types
  • Really powerful - allow to write logic inside our types
  • Similar to the regular JS ternary operator (inline conditions)
    • differences: in the syntax (extends keyword), check is done at compile time and not runtime
  • Syntax: T extends U ? X : Y
  • Example - customdt_/exerc_/e9
  • Exercise - customdt_/exerc_/ex8_9

Applying Decorators

  • Enabling decorators
  • Creating class, parameter, and method decorators
  • Using property descriptors
  • Using metadata

Reflection, tightly coupled with

  • Reflection is the capability of a certain piece of code to examine and be introspective about itself (navel-gazing)
    • a piece of code can have access to things such as the variables, functions, and classes defined inside it
  • Most languages provide some kind of reflection API that enables us to treat the code itself as if it was data
    • TypeScript is built upon JavaScript - inherits the JavaScript reflection capabilities

Decorators intro

  • Decorators (from js proposal)
    • can be used to metaprogram and add functionality to a value
    • without fundamentally changing its external behavior
  • Have three primary capabilities
    • Can replace the value that is being decorated with a matching value that has the same semantics
      • e.g. a method with another method, a field with another field, a class with another class, etc
    • Can provide access to the value that is being decorated via accessor functions (can be shared)
    • Can initialize the value that is being decorated, running additional code after the value has been fully defined
      • when the value is a member of class, initialized once per instance

Decorators intro con't

  • Special kind of declaration
  • Can be attached to
    • a class declaration, method, accessor, property, or parameter
  • Uses @expression
    • expression must evaluate to a function
    • such function will be called at runtime with information about the decorated declaration
  • To transpile
tsc --target ES5 --experimentalDecorators
  • tsconfig.json
"experimentalDecorators": true,                   /* Enable experimental support for TC39 stage 2 draft decorators. */
"emitDecoratorMetadata": true,                    /* Emit design-type metadata for decorated declarations in source files. */

Decorator types, syntax

@ClassDecorator
class ExampleClass {
    @PropertyDecorator
    public exampleProperty:number = 0;
    private _exampleField: number = 0;
    @AccessorDecorator
    public get exampleField() { return this._exampleField; }
    @MethodDecorator
    public exampleMethod(@ParameterDecorator paramName: string) {}
}

//// 'PascalCase' instead of 'lowerCamelCase' 
function ClassDecorator (constructor: Function) {}
function AccessorDecorator (target: any, propertyName: string, descriptor: PropertyDescriptor) {}
function MethodDecorator (target: any, propertyName: string, descriptor: PropertyDescriptor) {}
function PropertyDecorator (target: any, propertyName: string) {}
function ParameterDecorator (target: any, propertyName: string, parameterIndex: number) {}

Class Decorator

interface Invoice {
	id: string;
	clientId: number;
}

interface HasNewProperty {
  newProp: string;
}

// decorator definition can look like this
function SignedInv<T extends {new(...args:any[]):{}}>(constructor:T) {
    // return class extends constructor {
      return class extends constructor implements HasNewProperty {
        newProp = "new prop";
        invSign = "my_new_name_template";
    }
}

// Decorator 'factory' - common practice to pass custom params
function InvoiceDescr(limit: number) { 
  return function (constructor: Function) { 
    constructor.prototype.invType = 'Consultancy' + limit
  }
}

@SignedInv
@InvoiceDescr(3)
class FranchiseeAccountancyTool {
	private _invoice;
        invSign: string;

	constructor(public accToolKey: string, public taxRate: string) {
              this.invSign = accToolKey + 'inv_code';
	}

	get invoice() {
		return this._invoice;
	}

	set invoice(inv: Invoice) {
		this._invoice = inv;
	}
}

let franAcc = new FranchiseeAccountancyTool('cnaj837tjdhsu#jd9_fd8', '204');
console.log(franAcc);
console.log(franAcc.invSign);
console.log(franAcc.newProp);
console.log(franAcc.invType);

Class Decorator examples

Decorator exercises

  • Ex 1-5 (class, method, accessor)
  • Act1
  • Ex 6-8 (field, param)
    • metadata, with 'reflect-metadata' pollyfill-lib
  • Act2

Implementing Asynchronous Code and APIs

  • Using callbacks, promises, and async/await
  • Writing a REST API with Node.js and TypeScript

Using callbacks, promises, and async/await

  • JavaScript runtime is single threaded (on both web browser and server via node)
    • One, and only one, piece of code will be running at a particular time - main thread
  • JavaScript has also been built around an asynchronous approach
    • main thread will not pause when requested to load a resource of some sort
    • will place request onto an internal queue, eventually be processed at a later point in time
    • it does take away the need for in-memory locking mechanisms (other languages)

Callbacks, promises, and async/await con't

  • The callback mechanism - we provide a callback function to an asynchronous request
    • it will be executed once the asynchronous request has been processed
  • The Promise mechanism - provides a simplified syntax for writing asynchronous code
    • allows to chain multiple asynchronous calls one after another (fluent syntax)
  • Async and await technique - we mark certain functions as asynchronous
    • use the await keyword to pause the execution flow until the asynchronous function returns

Callbacks, promises, and async/await examples

  • Callbacks
    • async_/examp_/callbacks
  • Promises
    • async_/examp_/promises
  • Async/await
    • async_/examp_/async_and_await
  • Comparison of all approaches
    • async_/examp_/callback_vs_..

Callbacks, promises, and async/await exercises

  • Callbacks - async_/exerc_/ex1
  • Promises - async_/exerc_/ex2
    • Optional - async_/exerc_/a2
  • Ex3 - async/await
    • Optional - async_/exerc_/a3

Writing a REST API with Node.js and TypeScript

  • REST is a very common standard for web traffic
    • Most websites and web APIs operate using REST
  • Representational State Transfer
  • Defines concepts
    • operations ("methods" or "verbs") - GET, DELETE, POST, PUT, and PATCH
    • resources ("path" or "noun")
  • Example - server - rest_/e1
  • Exercises - client - rest_/ex1
    • Add missing functionalities
      • Reactjs - deleteOne, searchBy - other_/fe_/react-api-call-ts
    • Discussion/homework - migrate from JS to TS - other_/be_
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