TypeScript

Advantages of TS

• Static Typing => code is more predictable and easier to debug
• OOP => easier to organize code
• Compilation => errors are caught before runtime

Common Datatypes

• Number - All numeric values are represented by the number type, there aren't separate definitions for integers, floats or others.
• String - The text type, just like in vanilla JS strings can be surrounded by 'single quotes' or "double quotes".
• Boolean - true or false, using 0 and 1 will cause a compilation error.
• Any - A variable with this type can have it's value set to a string, number, or anything else.
• Arrays - Has two possible syntaxes: my_arr: number[]; or my_arr: Array<number>.
• Void - Used on function that don't return anything.

TypeScript: Handbook - Basic Types

Interfaces

Interfaces make sure an Object matches a specific structure. The order of the values does not matter.

interface Food {
    name: string;
    calories: number;
}

function speak(food: Food): void{
  console.log("Our " + food.name + " has " + food.calories + " calories.");
}

var ice_cream = {
  name: "ice cream", 
  calories: 200
}

speak(ice_cream);

TypeScript: Handbook - Interfaces

Classes

class Menu {
  items: Array<string>;
  pages: number;

  constructor(item_list: Array<string>, total_pages: number) {
    this.items = item_list;    
    this.pages = total_pages;
  }

  list(): void {
    console.log("Our menu for today:");
    for(var i=0; i<this.items.length; i++) {
      console.log(this.items[i]);
    }
  }
} 


// Inheritance

class HappyMeal extends Menu {
  constructor(item_list: Array<string>, total_pages: number) {
    super(item_list, total_pages);
  }

  list(): void{
    console.log("Our special menu for children:");
    for(var i=0; i<this.items.length; i++) {
      console.log(this.items[i]);
    }
  }

TypeScript: Handbook - Classes

Generics

Using generics instead of any makes sure the type of the input is preserved. With any, everything is converted to any

function genericFunc<T>(argument: T): T[] {    
  var arrayOfT: T[] = [];
  arrayOfT.push(argument);
  return arrayOfT;
}

var arrayFromString = genericFunc<string>("beep");
console.log(arrayFromString[0]);         // "beep"
console.log(typeof arrayFromString[0])   // String

var arrayFromNumber = genericFunc(42);
console.log(arrayFromNumber[0]);         // 42
console.log(typeof arrayFromNumber[0])   // number