Does “untyped” also mean “dynamically typed” in the academic CS world?

Question

I\'m reading a slide deck that states \"JavaScript is untyped.\" This contradicted what I thought to be true so I started digging to try and learn more.

Every answer

Answer 1

Untyped and dynamically typed are absolutely not synonyms. The language that is most often called "untyped" is the Lambda Calculus, which is actually a unityped language - everything is a function, so we can statically prove that the type of everything is the function. A dynamically typed language has multiple types, but does not add a way for the compiler to statically check them, forcing the compiler to insert runtime checks on variable types.

Then, JavaScript is a dynamically typed language: it is possible to write programs in JavaScript such that some variable x could be a number, or a function, or a string, or something else (and determining which one would require solving the Halting Problem or some hard mathematical problem), so you can apply x to an argument and the browser has to check at runtime that x is a function.