Is this a good solution to your problem?

Yeah, it worked. Thanks!

Hi,
I need to display a time.Duration and on my gopherjs install, a:

d, _ := time.ParseDuration("1m30s")
fmt.Println("%T, %v", d, d)
// prints: "int64, 90000000000"

And then, any attempt to call d.String() will be faced with: String is not a function

I tried on the gopherjs playground, and of course it doesn't have the same behavior. I have GopherJS 1.12-2. I don't know if it's linked to this issue or it's something else, and maybe I should open a new issue.

GopherJS tip (3e4dfb7) with Go 1.12.7 on my mac works for me:

package main

import (
	"fmt"
	"runtime"
	"time"
)

func main() {
	d, _ := time.ParseDuration("1m30s")
	fmt.Printf("%T, %v\n", d, d)
	fmt.Printf("%s\n", d)
	fmt.Printf("%s\n", d.String())
	fmt.Printf("%s\n", runtime.Version())
}

prints

% gopherjs run issue_32.go
time.Duration, 1m30s
1m30s
1m30s
go1.12.7
% gopherjs version
GopherJS 1.12-2

Maybe an upgrade would fix things?

Actually, to repeat my use case in a more similar way, I received a time.Duration in a struct unmarshaled from gob bytes. Trying to call this time.Duration's String() function failed with the String is not a function.

I found a workaround, which consists of:

durationWronglyConsideredAsInt64, _ := GetTimerDuration()
goodDuration := time.Duration(int64(durationWronglyConsideredAsInt64))

And then it's rightfully considered as time.Duration, and I can call .String() on it

(And I tried with just this, and it failed:

goodDuration := time.Duration(durationWronglyConsideredAsInt64)

)

What's the actual type returned by GetTimerDuration()? I mean, time.Duration is just an int64, so it's not like there's a complex struct that needs to be initialized (at least from the Go point of view; I think int64s are emulated in GopherJS as two int32's). If GetTimerDuration isn't returning a time.Duration, that seems like the problem right there.

If it is returning a time.Duration, well, I don't know what to tell you. That's weird.

Could you post a full main() function or link to the GopherJS playground that reproduces the problem?

Here is the gopherjs playground:
https://gopherjs.github.io/playground/#/ONanWJXXtL

And the equivalent go playground:
https://play.golang.org/p/91dh16Ry_BK

Y'all this is weird. From @dolanor's first gopherjs playground link:

type Message struct {
	Duration time.Duration
}

m := Message{Duration: time.Minute}

var buf bytes.Buffer
err := gob.NewEncoder(&buf).Encode(m)
if err != nil {
	panic(err)
}

m2 := Message{}
err = gob.NewDecoder(&buf).Decode(&m2)
if err != nil {
	panic(err)
}
fmt.Printf("m2 => type: %T, value: %v, decimal: %d\n", m2.Duration, m2.Duration, m2.Duration)
// prints m2 => type: int64 [should be time.Duration], value: 60000000000 [should be 1m0s], decimal: 60000000000 [this is fine]

So somehow the gob decoder is not setting the type of m2.Duration correctly.

Somebody that knows more gopherjs internals than I do is going to have to weigh on this. Sorry @dolanor. Might want to open a new issue.