How to load file repeatedly

[stellarhoof]

I've got a foo.ts file I'm editing and I want to .load foo.ts in the repl. First time works fine but subsequent times compilation fails because of Duplicate function implementation. I thought it was a cache issue but it also happens with ts-node --no-cache. Any way to clear compilation cache?

[stelcheck]

This happens because the function is already defined in the same context.

> .load a
function a() {}

{}
> function a() {}
Thrown: ⨯ Unable to compile TypeScript
[eval].ts (-1,10): Duplicate function implementation. (2393)
[eval].ts (1,10): Duplicate function implementation. (2393)
> delete a
Thrown: ⨯ Unable to compile TypeScript
[eval].ts (1,8): The operand of a delete operator must be a property reference. (2703)
> a  = undefined
Thrown: ⨯ Unable to compile TypeScript
[eval].ts (1,1): Cannot assign to 'a' because it is not a variable. (2539)

The REPL interface behaves the same way as a single ts file; the cache is a compile cache, and has nothing to do with what happens at runtime.

[stellarhoof]

Hmmm yeah you're right. I just thought .load would be smarter to invalidate all declarations beforehand.

[blakeembrey]

How does load work in node.js with constant variables? If that works, we can try and find a way around this. The other alternative (and related to a similar issue on the REPL) is to disable a set of warnings automatically when using the REPL.

[stelcheck]

> .load a.js
const a = 1;
 
undefined
> const a = 1;
SyntaxError: Identifier 'a' has already been declared

> 

[stellarhoof]

@stelcheck That is standard behavior yes. But the const redeclaration doesn't come from a .load. This is fine. What I'm looking for is a way for load to invalidate previous declarations when invoked. So in your example, since const a was already declared, it'd not error out, instead it'd overwrite the definition. But only on .load! I don't know if this is currently possible. Google has yielded nothing for me.

[stelcheck]

Since under the hood we use Node.js' REPL library - which, itself, is used when you run the actual node REPL - behaves as it does, I am not sure there would even be a way to do that for TypeScript. I hardly see how we would be able to keep track of which files define what ourselves TBH. Keep in mind that .load loads the file's code in the current context; once loaded, I doubt we'd have a proper way to figure out which method was defined by which file. At the very least, it would seem like a rather daunting task.

Of course, if you have any suggestions on how this would be implemented, I would be happy to help.

[cspotcode]

Today, users can avoid this issue via ts-node --transpile-only or ts-node --ignore-diagnostics 2393. This will suppress the "duplicate declaration" diagnostic.

In both the standard nodejs REPL and in ts-node, .load is like dot-sourcing or copy-pasting the loaded file's contents into a JS file. If you .load the following file twice in a row:

function foo() {}
const a = 123;

You get a REPL session that internally looks like:

function foo() {}
const a = 123;
function foo() {}
const a = 123;

node will throw an error because the const is redeclared. ts-node will throw the same error, but will also throw the TS diagnostic about a redeclared function. I think suppressing this diagnostic automatically would be incorrect, since users expect ts-node to typecheck. (unless they pass --transpile-only)

If we added magic to our REPL that invalidates previous declarations, this wouldn't be consistent with node's own REPL. I think this would also be incorrect. Plus it'd be super-complicated.

I feel pretty confident saying we can't / shouldn't do either of these solutions.

Closing to whittle down the list of open issues. If I'm wrong, let me know and I'll re-open.