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syscall/js: panic: not a number #26170

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agnivade opened this issue Jul 1, 2018 · 6 comments
Closed

syscall/js: panic: not a number #26170

agnivade opened this issue Jul 1, 2018 · 6 comments
Labels
arch-wasm WebAssembly issues FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker
Milestone
Go1.11

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@agnivade
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agnivade commented Jul 1, 2018

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version devel +6780042 Sun Jul 1 08:07:47 2018 +0000 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/agniva/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/agniva/play/go"
GOPROXY=""
GORACE=""
GOROOT="/home/agniva/play/gosource/go"
GOTMPDIR=""
GOTOOLDIR="/home/agniva/play/gosource/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build501975403=/tmp/go-build -gno-record-gcc-switches"
VGOMODROOT=""

What did you do?

I tried to rebuild my app after all the new changes in master. The app responds to events from input[type=range] and acts accordingly.

When I try to take the .Float() of the js.Value, I get the above-mentioned panic. The value is a perfectly fine float. And it even works fine if I take .String() and do a strconv.ParseFloat of it.

The problem goes away if I go back to the commit before 8997ec1 (syscall/js: use stable references to JavaScript values)

I believe this is an inadvertent mistake, please let me know if I am wrong.

What did you expect to see?

The app to run successfully after moving to new API.

What did you see instead?

panic: syscall/js: not a number
wasm_loader.js:39 
wasm_loader.js:39 goroutine 5 [running]:
wasm_loader.js:39 syscall/js.Value.Float(...)
wasm_loader.js:39 	/home/agniva/play/gosource/go/src/syscall/js/js.go:234
wasm_loader.js:39 main.main.func1(0x7ff8000000000020)
wasm_loader.js:39 	/home/agniva/play/go/src/github.com/agnivade/shimmer/repro.go:12 +0x11
wasm_loader.js:39 syscall/js.NewEventCallback.func1(0xc01e048, 0x1, 0x1)

Very minimal repro, without releasing callbacks -

<label for="contrast">Contrast</label>
<input type="range" min="-1" max="1" value="0" step="0.1" id="contrast">
// +build js,wasm

package main

import (
	"fmt"
	"syscall/js"
)

func main() {
	cb := js.NewEventCallback(js.PreventDefault, func(ev js.Value) {
		// This panics
		delta := ev.Get("target").Get("value").Float()
		fmt.Println(delta)

		// This works
		// deltaStr := ev.Get("target").Get("value").String()
		// delta, err := strconv.ParseFloat(deltaStr, 64)
		// if err != nil {
		// 	fmt.Println(err)
		// 	return
		// }
		// fmt.Println(delta)
	})
	js.Global().Get("document").
		Call("getElementById", "contrast").
		Call("addEventListener", "change", cb)

	select {}
}
@agnivade agnivade added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker arch-wasm WebAssembly issues labels Jul 1, 2018
@agnivade agnivade added this to the Go1.11 milestone Jul 1, 2018
@agnivade
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agnivade commented Jul 1, 2018

/cc @neelance

@neelance
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neelance commented Jul 1, 2018

The value of an <input type="range"> is a string, not a number, see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/range.

@myitcv
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myitcv commented Jul 1, 2018 via email

@agnivade
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agnivade commented Jul 1, 2018

I see. So it was a mistake earlier ? And strconv.ParseFloat() is the way to go ?

@neelance
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neelance commented Jul 1, 2018

@agnivade The earlier version did implicit type conversions, which got removed. You can try the valueAsNumber mentioned on the MDN page or strconv.ParseFloat().

@myitcv Yes, that's on my todo list.

@agnivade
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agnivade commented Jul 1, 2018

Thanks. Closing.

@agnivade agnivade closed this as completed Jul 1, 2018
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arch-wasm WebAssembly issues FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker
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