Hi , I will explain more with code example in my perl dancer code I have route ... $jsonFile ...

Sorry, that doesn't compile , its not perl

$ perl nope
Bareword found where operator expected at nope line 5, near ""{"name"
        (Missing operator before name?)
String found where operator expected at nope line 5, near "name":""
Bareword found where operator expected at nope line 5, near "":"jsonFi
+leexample"
        (Missing operator before jsonFileexample?)
String found where operator expected at nope line 5, near "jsonFileexa
+mple",""
Bareword found where operator expected at nope line 5, near "","proble
+m"
        (Missing operator before problem?)
String found where operator expected at nope line 5, near "problem":""
Bareword found where operator expected at nope line 5, near "":"thisIs
+ThrProblem"
        (Missing operator before thisIsThrProblem?)
Backslash found where operator expected at nope line 5, near "thisIsTh
+rProblem\"
String found where operator expected at nope line 5, at end of line
        (Missing semicolon on previous line?)
syntax error at nope line 5, near ""{"name"
Can't find string terminator '"' anywhere before EOF at nope line 5.
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in the server side I have the route that receive the perl dancer paramemters

That doesn't mention sendfileToserver

so here in javascript I had the error , that some thing is wrong with the json file when I look at the error I saw that json file is missing the \

So far you're not showing a problem with Dancer

Most likely a problem in your template