What is TypeScript?

• TypeScript is a typed super-set of JavaScript
  • It means that any JavaScript code is a legal TypeScript code
  • Also we can write any JavaScript code in a Typescript file (.ts) without any error
  • It add rules about how different type of values can be used
  • It preserves the run-time behavior of JavaScript code, which means that TypeScript will not throw any “type” errors on run-time
• TypeScript is a static type checker for JavaScript
  • Detecting errors in code without running is known as static checking
  • Determining the nature or type of error based on the type of values is known as static type checking
  • So TypeScript checks a program for errors before execution based on the type of values
• So the bottom line is that
  • We can use TypeScript to develop our JavaScript programs
    • TypeScript provides types, classes and OOP concepts
    • TypeScript give details about errors or warnings produced by the code before the execution of the code
    • It highlights the unexpected behavior in code, lowering the chance of bugs
  • Then TypeScript compiler converts the code back to JavaScript code without the TYPES information

//Example Code:

const obj = { width: 10, height: 15 };
const area = obj.width * obj.heigth;

Error: Property ‘heigth’ does not exist on type ‘{ width: number; height: number; }’. Did you mean ‘height’?

Above code will produce this error in TypeScript

Types in TypeScript

• TypeScript (TS) can infer types from existing JavaScript (JS) variables using their values
  • So TS automatically assign types to the existing JS code
  • Which means that now TS will warn us about warnings or errors in the JS code before execution (Excellent! Not?)
• TS also allows to define types manually
• TS provides Unions and Generics to create complex types combining simple types

References:

• https://www.typescriptlang.org/docs/handbook/typescript-from-scratch.html