Learning TypeScript

Chapter 14. Syntax Extensions

“TypeScript does not add

to the JavaScript runtime.”

…​was that all a lie?!

When TypeScript was first released in 2012, web applications were growing in complexity faster than plain JavaScript was adding features that supported the deep complexity. The most popular JavaScript language flavor at the time, CoffeeScript, had made its mark diverging from JavaScript by introducing new and exciting syntactic constructs.

Nowadays, extending JavaScript syntax with new runtime features specific to a superset language such as TypeScript is considered bad practice for several reasons:

• Most importantly, runtime syntax extensions might conflict with new syntax in newer versions of JavaScript.

• They make it more difficult for programmers new to the language to understand where JavaScript ends and other languages begin.

• They increase complexity of transpilers that take superset language code and emit JavaScript.

Thus, it is with a heavy heart and deep regret that I must inform you that the early TypeScript designers introduced three syntax extensions to JavaScript in the TypeScript language:

• Classes, which aligned with JavaScript classes as the spec was ratified

• Enums, a straightforward syntactic sugar akin to a plain object of keys and values

• Namespaces, a solution predating modern modules to structure and arrange code

Note

TypeScript’s “original sin” of runtime syntax extensions to JavaScript is fortunately not a design decision the language has ...