Question: Avoiding error identifier has already been declared

[jmatsushita]

What's the elegant way to avoid having these popping up? The ways I know work are:

• Restart the kernel.
• Just clearing the output and pretend it didn't happen

The way I tried which didn't work for me are:

• Avoid restarting all
• Avoid restarting cells with const in it
• Not use const

:)

[n-riesco]

First of all, I have to say this is the expected behaviour: const was introduced in JS to ensure a variable doesn't get reassigned (Note that, similarly, let doesn't allow the re-declaration of a variable). The use of const or let inside the global scope will prevent you from re-running a cell (unless the kernel session is restarted).

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Since IJavascript is a JS kernel and const is part of JS, I think a kernel like jp-babel would be a more suitable kernel for the needs I can infer from your post.

I imagine one could write a plugin that replaces all const's and let's in the global scope by var's, so that no exceptions is thrown when a cell is re-run without restarting the kernel session.

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Out of curiosity: you say that "Not use const" "didn't work for you". Why was that?

[n-riesco]

I'm closing the issue, but, please, feel free to continue the discussion here.

[Nithanaroy]

const makes sense. But I would use redefine a class interactively making changes. How can we achieve that? In Scala kernel, rerunning a cell say with val a = 10 doesn't throw any error, but instead overrides it. But of course if we try a = 20 later it complains as expected. Can this behavior be achieved?

[n-riesco]

@Nithanaroy What I wrote above still applies. I don't see how to achieve this without parsing each execution request:

• jp-babel is an example of a kernel with such a parser
• ijavascript-await is an old experimental fork of IJavaScript that also uses a parser to implement await at REPL level.