# A JS backend bug... workaround? **URL:** \ **Category:** Uncategorized\ **Created:** [August 19, 2014, 7:49pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507 "2014-08-19T19:49:02Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![RobNik](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@RobNik](https://discuss.kotlinlang.org/u/RobNik)\ **Post date:** [August 19, 2014, 7:49pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/1 "2014-08-19T19:49:02Z")
Any idea what might be causing this? I'll work on trying to narrow it down. I have code like :   for (p in people) {   …   td {   a {               href = “doSomething?id=${p.id}”            className = “red”            +p.name   }   } Those functions `td` and `a` are builders, taking extension function/closures as their last argument.  The generated js is doubled, as you see below, and it crashes.  `p_0` is undefined.   f\_18: function (p) {            return function () {            this.href = ‘doSomething?id=’ + p.id;            this.className = ‘red’;            _.mymod.plus(p.name);_ _           this.href = ‘doSomething?id=’ + p\_0.id;            this.className = ‘red’;                               _.mymod.plus(p\_0.name);            };   }, Rob ---
**Author:** ![bashor](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/bashor/32/1431_2.png) [@bashor](https://discuss.kotlinlang.org/u/bashor)\ **Post date:** [August 19, 2014, 8:11pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/2 "2014-08-19T20:11:25Z")
Could you provide more informations?   - your project or minimal code for reproduce;   - compiler version. It looks like bug, feel free to [create issue in our tracker](http://youtrack.jetbrains.com/newIssue?project=KT) with details. Thanks! ---
**Author:** ![bashor](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/bashor/32/1431_2.png) [@bashor](https://discuss.kotlinlang.org/u/bashor)\ **Post date:** [August 19, 2014, 8:18pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/3 "2014-08-19T20:18:40Z")
I could not reproduce it on [kotlin-demo](http://kotlin-demo.jetbrains.com/) with: ```kotlin trait People {   val id: Int   val name: String } trait A {   var href: String   var className: String   fun String.plus() } trait TD {   fun a(f: A.() -> Unit) } fun td(f: TD.() -> Unit) {} fun test(people: List) {   for (p in people) {   td {   a {               href = “doSomething?id=${p.id}”            className = “red”            +p.name   }   }   } } ``` ---
**Author:** ![RobNik](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@RobNik](https://discuss.kotlinlang.org/u/RobNik)\ **Post date:** [August 20, 2014, 12:49am UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/4 "2014-08-20T00:49:23Z")
I sent you some code via email. Didn't want to post here in case I accidentally include too much. Rob ---
**Author:** ![bashor](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/bashor/32/1431_2.png) [@bashor](https://discuss.kotlinlang.org/u/bashor)\ **Post date:** [August 20, 2014, 11:52am UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/5 "2014-08-20T11:52:56Z")
I can't reproduce problem with your project too. Please tell us your Kotlin compiler version. And please check the code that I wrote above on your environment. Thanks. ---
**Author:** ![RobNik](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@RobNik](https://discuss.kotlinlang.org/u/RobNik)\ **Post date:** [August 20, 2014, 12:12pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/6 "2014-08-20T12:12:53Z")
I'm running IDEA 13 CE, Kotlin plugin 0.8.11.  Your example code above compiles fine and does not produce the duplicate JS. Rob ---
**Author:** ![RobNik](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@RobNik](https://discuss.kotlinlang.org/u/RobNik)\ **Post date:** [August 20, 2014, 12:45pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/7 "2014-08-20T12:45:11Z")
There are some warnings about core/javautil.kt that always appear when I run the JS backend. I figured I could ignore them, but just in case there is something is wrong with my installation, here is the compiler output: Information:Kotlin: Kotlin JPS plugin version 0.8.11 Information:Kotlin: Using kotlinHome=/Users/rob/Library/Application Support/IdeaIC13/Kotlin/kotlinc Information:Kotlin: Invoking K2JSCompiler with arguments -tags -verbose -version -printArgs -output /Users/rob/Workspace/KotlinBugs/Bug1/out/production/Bug1/Bug1.js -libraryFiles /Users/rob/Workspace/KotlinBugs/Bug1/lib/kotlin-jslib.jar -sourceFiles /Users/rob/Workspace/KotlinBugs/Bug1/src/kotlinbug1/HtmlBuilders.kt,/Users/rob/Workspace/KotlinBugs/Bug1/src/kotlinbug1/Misc.kt,/Users/rob/Workspace/KotlinBugs/Bug1/src/kotlinbug1/ProjectList.kt,/Users/rob/Workspace/KotlinBugs/Bug1/src/kotlinbug1/Theirs.kt,/Users/rob/Workspace/KotlinBugs/Bug1/src/kotlinbug1/bugs/Bugs.kt Information:Kotlin: Kotlin Compiler version 0.8.11 Information:Module “Bug1” was fully rebuilt due to project configuration/dependencies changes Information:Compilation completed successfully with 8 warnings in 9 sec Information:0 errors Information:8 warnings Warning:Kotlin: ‘E’ has a nullable upper bound. This means that a value of this type may be null. Using ‘E?’ is likely to mislead the reader (core/javautil.kt (70:25)) Warning:Kotlin: ‘E’ has a nullable upper bound. This means that a value of this type may be null. Using ‘E?’ is likely to mislead the reader (core/javautil.kt (71:25)) Warning:Kotlin: ‘V’ has a nullable upper bound. This means that a value of this type may be null. Using ‘V?’ is likely to mislead the reader (core/javautil.kt (97:42)) Warning:Kotlin: Projection is redundant: the corresponding type parameter of Map has the same variance (core/javautil.kt (100:46)) Warning:Kotlin: ‘V’ has a nullable upper bound. This means that a value of this type may be null. Using ‘V?’ is likely to mislead the reader (core/javautil.kt (101:45)) /Users/rob/Workspace/KotlinBugs/Bug1/src/kotlinbug1/ProjectList.kt Warning:(22, 17) Kotlin: Variable ‘row’ is never used Warning:(41, 9) Kotlin: Variable ‘pl’ is never used /Users/rob/Workspace/KotlinBugs/Bug1/src/kotlinbug1/Theirs.kt Warning:(22, 8) Kotlin: Parameter ‘f’ is never used ---
**Author:** ![bashor](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/bashor/32/1431_2.png) [@bashor](https://discuss.kotlinlang.org/u/bashor)\ **Post date:** [August 20, 2014, 12:49pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/8 "2014-08-20T12:49:33Z")
You are right it's not your problem, it's problem in stdlib. ---
**Author:** ![bashor](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/bashor/32/1431_2.png) [@bashor](https://discuss.kotlinlang.org/u/bashor)\ **Post date:** [August 20, 2014, 7:54pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/9 "2014-08-20T19:54:08Z")
I simplified your code to: ```kotlin ... fun test(flag: Boolean) {   buildTr {   td {            a {            global += “1”            }   }   td {            a {            href = “something” + if(flag) “a” else “b” // workaround: //           val tmp = if(flag) “a” else “b” //           href = “something” + tmp            }   }   } } ``` This and your code works fine on current master. So You can apply workaround or update your compiler. Thanks for your report! ---
**Author:** ![RobNik](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@RobNik](https://discuss.kotlinlang.org/u/RobNik)\ **Post date:** [August 20, 2014, 7:57pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/10 "2014-08-20T19:57:31Z")
Thank you.  I'm curious, so you were able to reproduce the bug in the older version? Rob ---
**Author:** ![bashor](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/bashor/32/1431_2.png) [@bashor](https://discuss.kotlinlang.org/u/bashor)\ **Post date:** [August 20, 2014, 8:06pm UTC](https://discuss.kotlinlang.org/t/a-js-backend-bug-workaround/507/11 "2014-08-20T20:06:59Z")
Yes,I reproduced it on IDEA 13 with Kotlin M8.