Earlier quoted context omitted.
It's not common now! The software world is huge; a niche of a niche is not some bellwether of the industry.
> It's not common now! It is [1]. Over 60% of Javascript developers use it somewhere, and over 1/3rd of all developers use it for something. Almost all widely used npm modules have @types annotations as well. Outside of node, it's arguably the most ubiquitous voluntary extension of the JS ecosystem ever. [1] https://redmonk.com/jgovernor/2019/05/07/typescriptexploding...
Common among JS developers != common among programmers != common among professionals in the software industry