Add flag --hide-execution-result

[JocelynDelalande]

See that example:

I understand that ijavascript outputs the value of the latest affected variable (so displaying 11, which is the value of i).

But in the context of teaching programming basics, this is very confusing ("why does it counts till 11 instead of 10 ?" ).

So…

Short-term question

Is there a way to disable this behavior ?

Long-term question

Is this behavior desirable at all ?

FYI, ipython python core does not have this behavior:

Thanks by advance :-)

[rgbkrk]

This is part of JavaScript itself. If you try the same in the node console or in devtools for Chrome or Firefox, you'll get the same:

REPLs show the last result of the code. What's peculiar is that JavaScript while loops and blocks have a result. The result of a block is the result of the last statement in the block ({1; 2} --> 2). The result of a while statement is the result of the last iteration of the statement.

[rgbkrk]

In case you were curious, the same applies to for loops too:

[JocelynDelalande]

@rgbkrk ok, very interesting.

So my only (reasonable) way here seems to be disabling the display of all execution results, I have to search on that.

I left this issue open for a few days in case someone comes with something better.

[n-riesco]

@JocelynDelalande to avoid this JS behaviour, you could rewrite your code like this:

var i = 0;
while(i < 10) {
    console.log(i++);
}

[JocelynDelalande]

Nicolas Riesco notifications@github.com wrote:

@JocelynDelalande to avoid this JS behaviour, you could rewrite your code like this:

var i = 0;
while(i < 10) {
    console.log(i++);
}

@n-riesco Thanks, but for a gentle introduction to algorithmics, this is pretty hardcore stuff :-).

[n-riesco]

@JocelynDelalande Oh, I see. In that case, I'd use a for-loop:

for(var i = 0; i < 10; i++) {
    console.log(i);
}

[JocelynDelalande]

@n-riesco yes, but in this very case, my point si to show/experiment the while loop.

I'm trying to adapt the tools for the teaching, not the teaching to to the tools :-)

@n-riesco any idea/lead on how to disable the display of the latest evaluated expression in ijavascript notebooks ?

[n-riesco]

@n-riesco yes, but in this very case, my point si to show/experiment the while loop.

I'm trying to adapt the tools for the teaching, not the teaching to to the tools :-)

@n-riesco any idea/lead on how to disable the display of the latest evaluated expression in ijavascript notebooks ?

The idea behind the examples I've given above is to ensure the last statement returns undefined (by default ijsinstall installs the IJavascript kernel with the flag --hide-undefined).

I could implement a flag to hide execution results (e.g. --hide-execution-result). I don't see any harm with such an option.

Alternatively, one could develop an nbextension to hide execution results (like https://github.com/ipython-contrib/jupyter_contrib_nbextensions/tree/master/src/jupyter_contrib_nbextensions/nbextensions/hide_input_all). This approach would work regardless the kernel.

[JocelynDelalande]

@n-riesco great, thanks :-)

[n-riesco]

@JocelynDelalande I haven't published a new release in npm yet. I wanted to update IJavascript's documentation before making a new release. But, if you're a going to use this feature straight away, I could make a release today.

[JocelynDelalande]

I'm fine, I'll maybe use it in several months :-)