Introduction to TypeScript

Last updated on 1 Feb, 2022

TypeScript is a syntactic superset of JavaScript. It means, it starts with basic JavaScript syntax, and then start building more type specific syntax on top of it. TypeScript is an open-source project maintained by Microsoft. The main goal is to add types to JavaScript.

Here is an example TypeScript code to declare a string type variable.

let name: string;

A TypeScript code is compiled by a TypeScript compiler and outputs JavaScript code.

Why Choose TypeScript?

One reason is developers can be bring their intent to the code. For example, below function is to add 2 numbers, NOT to concatenate 2 strings.

function add(a, b) {
  return a + b;
}

But how to express our intent? We can do using TypeScript.

function add(a: number, b: number): number {
  return a + b;
}

Now if somebody use the function like add("b", 3), TypeScript compiler will throw an error.

Second reason is TypeScript can detect some errors at compile time rather than at run time. Examples are:

  • Errors occuring due to null or undefined values in variables
  • Bad reference variables. You changed the name of a function, but forgot to replace the new name in all occurences.
  • Breakage around internal code contract. ie, earlier an argument was optional, but now it is mandatory.

Third reason is the code development experience with TypeScript. TypeScript gels well with Visual Studio Code. Both are from Microsoft. When working with TypeScript, the intellisense support and documentation support is great.

TypeScript Online Editor

If you want to try TypeScript syntax quickly, TypeScript language provides an online editor at https://www.typescriptlang.org/play. Also https://www.typescriptlang.org/ is the official website of TypeScript.

Typed Future JavaScript

Another question that comes to developers is about future JavaScript. Will JavaScript in near future bring type support? I don't think so.

Assume, JavaScript bring following syntax tomorrow:

string name = "Jack";

It is going to break a lot of JavaScript code floating on web starting from 90s. So it is good and advisable to learn TypeScript.