[elm-discuss] Elm Textfield + a barcode scanner

Discussion:

Chris Van Vranken

2017-04-28 14:51:48 UTC

I'm using a barcode scanner to enter data into an elm textfield. The
barcode scanner basically works like a keyboard with a user that makes very
rapid keystrokes. This rapid entry causes random characters to be missing
in the textfield. If the scan is supposed to enter "50494'', one or more
of these characters will often be missing. Using the debugger I see that
my model has values for that field that change from "5" to "50" to "504" to
"509" to "5094", but it should be "5" to "50" to "504" to "5049" to
"50494" So it ends up replacing "504" with "509" instead of with "5049".
I believe this is a threading issue where two events are firing in
parallel instead of in sequence, and both events are starting with the same
model data ("50") with the output of one event replacing the output of the
other, when instead the output model for one event should be the input for
the next event. Is this a bug in Elm? How do I fix this?

Thanks,
Chris

Simon

2017-04-28 15:06:03 UTC

Permalink

not sure whether this is relevant but can you take advantage of the
difference between the `oninput` and `onchange` events in a text field?

Post by Chris Van Vranken
I'm using a barcode scanner to enter data into an elm textfield. The
barcode scanner basically works like a keyboard with a user that makes very
rapid keystrokes. This rapid entry causes random characters to be missing
in the textfield. If the scan is supposed to enter "50494'', one or more
of these characters will often be missing. Using the debugger I see that
my model has values for that field that change from "5" to "50" to "504" to
"509" to "5094", but it should be "5" to "50" to "504" to "5049" to
"50494" So it ends up replacing "504" with "509" instead of with "5049".
I believe this is a threading issue where two events are firing in
parallel instead of in sequence, and both events are starting with the same
model data ("50") with the output of one event replacing the output of the
other, when instead the output model for one event should be the input for
the next event. Is this a bug in Elm? How do I fix this?
Thanks,
Chris

Chris Van Vranken

2017-04-28 16:47:34 UTC

Permalink

I'm using the oninput event, the onchange event occurs when the element
loses focus. The contents of the textbox are wrong before the onchange
event even fires, so I don't believe the onchange event will be helpful for
solving this. I think maybe I need to prevent elm from modifying the value
of the textbox and then read in the final value when the scanner sends the
enter key, which it does every time it finishes scanning the barcode.

Post by Simon
not sure whether this is relevant but can you take advantage of the
difference between the `oninput` and `onchange` events in a text field?

Bernardo

2017-04-29 17:19:22 UTC

Permalink

You should definitely try with onchange. But without using oninput because
otherwise the field is updated from the model. If you update the model
after the field changes there shouldn't be any difference from using a
plain html input.

Post by Chris Van Vranken
I'm using the oninput event, the onchange event occurs when the element
loses focus. The contents of the textbox are wrong before the onchange
event even fires, so I don't believe the onchange event will be helpful for
solving this. I think maybe I need to prevent elm from modifying the value
of the textbox and then read in the final value when the scanner sends the
enter key, which it does every time it finishes scanning the barcode.

Post by Simon
not sure whether this is relevant but can you take advantage of the
difference between the `oninput` and `onchange` events in a text field?

Francesco Orsenigo

2017-04-29 21:57:24 UTC

Permalink

This is an interesting problem and I wonder if it would happen also with
some other form of automated input (say, selenium).

It might very well be a problem with Elm.

Witold Szczerba

2017-04-29 22:28:52 UTC

Permalink

This was my case with Selenium WebDriver and Chrome. The end-to-end tests
of my Elm application are failing because of this.
It was reported back in 2014:
https://github.com/elm-lang/elm-compiler/issues/835
The issue is closed, but the bug is still present.

You want to know my workaround? It "just-works" on Firefox, so this is the
browser I use for e2e testsâŠ

On Sat, Apr 29, 2017 at 11:57 PM, Francesco Orsenigo <

Post by Francesco Orsenigo
This is an interesting problem and I wonder if it would happen also with
some other form of automated input (say, selenium).
It might very well be a problem with Elm.

Post by Chris Van Vranken
I'm using a barcode scanner to enter data into an elm textfield. The
barcode scanner basically works like a keyboard with a user that makes very
rapid keystrokes. This rapid entry causes random characters to be missing
in the textfield. If the scan is supposed to enter "50494'', one or more
of these characters will often be missing. Using the debugger I see that
my model has values for that field that change from "5" to "50" to "504" to
"509" to "5094", but it should be "5" to "50" to "504" to "5049" to
"50494" So it ends up replacing "504" with "509" instead of with "5049".
I believe this is a threading issue where two events are firing in parallel
instead of in sequence, and both events are starting with the same model
data ("50") with the output of one event replacing the output of the other,
when instead the output model for one event should be the input for the
next event. Is this a bug in Elm? How do I fix this?
Thanks,
Chris

Francesco Orsenigo

2017-04-29 22:52:20 UTC

Permalink

Witold, could you put together a minimal Elm app + Selenium script that
reproduces the problem?
This might be a significant issue, since it would impact the possibility to
end-to-end test Elm apps.

Post by Witold Szczerba
This was my case with Selenium WebDriver and Chrome. The end-to-end tests
of my Elm application are failing because of this.
It was reported back in 2014: https://github.com/elm-
lang/elm-compiler/issues/835
The issue is closed, but the bug is still present.
You want to know my workaround? It "just-works" on Firefox, so this is the
browser I use for e2e testsâŠ
On Sat, Apr 29, 2017 at 11:57 PM, Francesco Orsenigo <

Post by Francesco Orsenigo
This is an interesting problem and I wonder if it would happen also with
some other form of automated input (say, selenium).
It might very well be a problem with Elm.

Post by Chris Van Vranken
I'm using a barcode scanner to enter data into an elm textfield. The
barcode scanner basically works like a keyboard with a user that makes very
rapid keystrokes. This rapid entry causes random characters to be missing
in the textfield. If the scan is supposed to enter "50494'', one or more
of these characters will often be missing. Using the debugger I see that
my model has values for that field that change from "5" to "50" to "504" to
"509" to "5094", but it should be "5" to "50" to "504" to "5049" to
"50494" So it ends up replacing "504" with "509" instead of with "5049".
I believe this is a threading issue where two events are firing in parallel
instead of in sequence, and both events are starting with the same model
data ("50") with the output of one event replacing the output of the other,
when instead the output model for one event should be the input for the
next event. Is this a bug in Elm? How do I fix this?
Thanks,
Chris

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Noah Hall

2017-04-29 22:57:30 UTC

Permalink

A known issue: https://github.com/elm-lang/html/issues/55

The issue is elm-compiler was likely closed due to the fact that it is
not a compiler problem, it is a web-browser problem.

`defaultValue` is the recommended approach

On Sun, Apr 30, 2017 at 12:52 AM, Francesco Orsenigo

Post by Francesco Orsenigo
Witold, could you put together a minimal Elm app + Selenium script that
reproduces the problem?
This might be a significant issue, since it would impact the possibility to
end-to-end test Elm apps.

Post by Witold Szczerba
This was my case with Selenium WebDriver and Chrome. The end-to-end tests
of my Elm application are failing because of this.
https://github.com/elm-lang/elm-compiler/issues/835
The issue is closed, but the bug is still present.
You want to know my workaround? It "just-works" on Firefox, so this is the
browser I use for e2e tests…
On Sat, Apr 29, 2017 at 11:57 PM, Francesco Orsenigo

Post by Francesco Orsenigo
This is an interesting problem and I wonder if it would happen also with
some other form of automated input (say, selenium).
It might very well be a problem with Elm.

Post by Chris Van Vranken
I'm using a barcode scanner to enter data into an elm textfield. The
barcode scanner basically works like a keyboard with a user that makes very
rapid keystrokes. This rapid entry causes random characters to be missing
in the textfield. If the scan is supposed to enter "50494'', one or more of
these characters will often be missing. Using the debugger I see that my
model has values for that field that change from "5" to "50" to "504" to
"509" to "5094", but it should be "5" to "50" to "504" to "5049" to "50494"
So it ends up replacing "504" with "509" instead of with "5049". I believe
this is a threading issue where two events are firing in parallel instead of
in sequence, and both events are starting with the same model data ("50")
with the output of one event replacing the output of the other, when instead
the output model for one event should be the input for the next event. Is
this a bug in Elm? How do I fix this?
Thanks,
Chris

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Witold Szczerba

2017-04-30 00:36:41 UTC

Permalink

My issue was with regular input type=text fields.
I will try to find some time to create a project reproducing the issue.

Post by Noah Hall
A known issue: https://github.com/elm-lang/html/issues/55
The issue is elm-compiler was likely closed due to the fact that it is
not a compiler problem, it is a web-browser problem.
`defaultValue` is the recommended approach
On Sun, Apr 30, 2017 at 12:52 AM, Francesco Orsenigo

Post by Francesco Orsenigo
Witold, could you put together a minimal Elm app + Selenium script that
reproduces the problem?
This might be a significant issue, since it would impact the possibility

Post by Francesco Orsenigo
end-to-end test Elm apps.

Post by Witold Szczerba
This was my case with Selenium WebDriver and Chrome. The end-to-end

tests