There are quite a few differences from the old &quot;JScript&quot; days.<p>First of all: TypeScript is liberally licensed open source. JScript was totally proprietary.<p>Another aspect is that TypeScript is seeking to be a strict superset of JavaScript that evolves as JavaScript does (something that wasn&#x27;t really happening in the JScript days) and is focused on specifically providing static types and tooling for types in JS. It&#x27;s not a general &quot;embrace, extend, extinguish&quot; kind of thing at all, but rather a very targeted tool.<p>TypeScript is really one of the most JavaScript-y languages that compile to JS. Most of the compile-to-JS languages are more radical divergences from JS.<p>JS is not going to be replaced (though WebAssembly[1] will likely become an additional compile target), but compile-to-JS is going to continue to grow in popularity. Already, many people are compiling future-JS to present-day-JS.<p>The browser vendors have found that the standards evolve best when people can actually write code against the standards <i>before</i> the standards are hardened. Compile-to-JS tools help with that. If optional static types and type inference become very popular via TypeScript and Flow, JS itself may evolve to support those features and then we&#x27;ll have that standard.<p>Microsoft is a better player on the web today than they have ever been before.<p>[1]: <a href="https:&#x2F;&#x2F;github.com&#x2F;WebAssembly&#x2F;design" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;WebAssembly&#x2F;design</a>