[hombre_fatal]

To be fair, that's valid in Typescript because it simply uses Javascript's coercion rules.

You could imagine it having built-in rules for JS' coercions:

    string + number -> string
    number + string -> string

Maybe your snippet is provocative to some people, but in real code it would quickly fail once you actually use `bar` and were wrong about your assumptions.

At which point it's similar to languages with `Int + Float -> Float` and `Short + Long -> Long` in that perhaps you wish those operators weren't defined but it's at least consistent. And you'd find the error once you've passed those results to a function that expected Int or Short.

[pas]

It's not the fall, but the stop that kills you. So in case of TS we don't know what was the intent.

Maybe it was this.

function suffixWith10(s: string) { return s + 10; }

But if the intent can be discovered by analysis of usages of the variable later in the code, then TS will scream loudly.

[chc]

This is more of a knock against the compromises TypeScript's wacky type system has to make for JavaScript compatibility than anything else. It's not possible in a language that was really designed for strong static typing like Haskell or Rust.