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TypeScript   (PDF)
Posted February 9th, 2024

TypeScript is typed javascript that compiles to javascript It reduces errors in javascript.
These are basic takeaways from reading about typescript
So typescript is compiled javascript with strict typing.

1) Install typescript
npm i -g typescript
2) Check version
tsc -v
3) Compile stuff in .ts files to .js files
tsc -w

4) Defining variables
     let varname: type = default_value;
   types can be string, number, bigint, bool, null, undefined, symbol
   wrappers String,Number,BigInt, Boolean, Symbol
   union type: example : let foo: string|number=5;

   "any" type - not recommended - reverts to straight javascript
   const foo = document.querySelector('a')!;
   ! - indicates - non-null assertion to inform compiler
   type casting:
   const foo = document.getElementById('foobar') as HTMLFormElement;
   let flavors: 'chocolate'|'strawberry'|'blueberry';
5) reference types - arrays, objects, functions
  a) arrays
      let myarray: number[] = [1,2,4,5];
      let myarray: (number|boolean)[] = [1,true,2];
  b) tuples
      let mytuple: [string,number,boolean] = ['Danny,1,true];
  c) objects
     let person: {
          name: string;
     alive: boolean;
     person = { name:"Tom"; alive:true}; = "Mike";
  3) interfaces
     interface Person
        name: string;
    sayBye(name:string) => string;

     let something:Person {
        sayHi: function (name:string)
        return 'Hi ${name}';
       let person1:Person { name:"mike",alive:true};
  d) functions
     function funcname(arg1:type,arg2?:type):return_type
     or with es6
          const funcname = (arg1:type,arg2?:type):return_type =>
     ? means optional argument.   
     let funcname: (arg1:type):null;
  e) types
      type PersonObject= {
     age: number;

  f) classes
        class classname {
       private name: string;
        protected age: number;
        constructor(n:string,a:number) {
 = n;
          this.age = a;
        display() {
            return "Name: ${} age:${this.age}";

     let people: Person[] = [person1,person2];

    definition of scope of variables:
     readonly name: string; // This property is immutable - it can only be read
     private isCool: boolean; // Can only access or modify from methods within this class
     protected email: string; // Can access or modify from this class and subclasses
      public pets: number; // Can access or modify from anywhere - including outside the class

   g) generics
      const addID = (obj: T) => {
      let id = Math.floor(Math.random() * 1000);

      return { ...obj, id };
     interface hasLength {
      length: number;

     function logLength(a: T) {
       return a;

  h) enums
      enum states { AL="AL",


6. typescript interacts with multiple react platforms:

  •     create-react-app (TS setup)
  •     Gatsby (TS setup) Next.js
  •     Next.js (TS setup)
  • Concise tutorial:

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