How to get JavaScript caller function line number How to get JavaScript caller source URL

Question

I am using the following for getting the JavaScript caller function name   var callerFunc   arguments callee caller toString    callerFuncName    callerFunc substring callerFunc indexOf  function     8  callerFunc indexOf           anoynmous     Is there a way to discover the line number from which the method was called   Also  is there a way to get the name of the JavaScript file the method was called from  Or the source URL

User · Answer

This is often achieved by throwing an error from the current context; then analyzing error object for properties like lineNumber and fileName (which some browsers have)

function getErrorObject(){
  try { throw Error('') } catch(err) { return err; }
}

var err = getErrorObject();

err.fileName;
err.lineNumber; // or `err.line` in WebKit

Don't forget that callee.caller property is deprecated (and was never really in ECMA 3rd ed. in the first place).

Also remember that function decompilation is specified to be implementation dependent and so might yield quite unexpected results. I wrote about it here and here.

User · Answer

My contribution to custom errors in JavaScript    First  I agree with this  B T guy at Inheriting from the Error object - where is the message property   we have to built it properly  actually you have to use a js object library  my favorite  https   github com jiem my-class    window g3   window g3        g3 Error   function  message  name  original         this original   original       this name   name     Error g3        this message   message     A g3 Error was thrown          original   this stack   this original stack  this stack   null       this message      lt br gt ---STACK--- lt br gt     this stack        var ClassEmpty   function        ClassEmpty prototype   Error prototype   g3 Error prototype   new ClassEmpty     g3 Error prototype constructor   g3 Error   then  we should define a global error handling function  optional  or  they ll end up to the engine   window onerror   printError   function printError msg  url  line       document getElementById  test   innerHTML   msg   lt br gt at    url   lt br gt line    line      return true     finally  we should throw our custom errors carefully     hit it    throw new g3 Error  Hey  this is an error message     Error Factory g3    throw new g3 Error  Hey  this is an error message     Error Factory g3   new Error        Only  when passing the third parameter as new Error   we are able to see the stack with function and line numbers   At 2  the function can also handle error thrown by the engine as well   Of course  the real question is if we really need it and when  there are cases  99  in my opinion  where a graceful return of false is enough and leave only some critical points to be shown with the thrown of an error   Example  http   jsfiddle net centurianii m2sQ3 1

User · Answer

To determine which line something is on you have to search all the code for the code that occupies the particular line of interest and count the   n  characters from the top to this of interest and add 1   I am actually doing this very thing in an application I am writing   It is a best practices validator for HTML and is still heavily under development  but the error output process that you would be interested in is complete   http   mailmarkup org htmlint htmlint html

User · Answer

I was surprised that most of these answers assumed that you wanted to handle an error rather than just output helpful debug traces for normal cases as well     For example  I like using a console log wrapper like this   consoleLog   function msg     See https   stackoverflow com a 27074218 470749     var e   new Error        if   e stack          try                  IE requires the Error to actually be thrown or else the                 Error s  stack  property is undefined              throw e            catch  e                if   e stack                      return 0     IE  lt  10  likely                             var stack   e stack toString   split   r n  n        if  msg                   msg                   console log msg                  stack 1                      This ends up printing an output such as the following to my console   1462567104174           getAllPosts http   me com helper js 362 9   See https   stackoverflow com a 27074218  and also A proper wrapper for console log with correct line number

User · Answer

This is how I have done it  I have tested it in both Firefox and Chrome  This makes it possible to check the filename and line number of the place where the function is called from   logFileAndLineNumber new Error      function logFileAndLineNumber newErr       if navigator userAgent indexOf  Firefox      -1             var originPath   newErr stack split   n   0  split             var fileNameAndLineNumber   originPath originPath length - 1  split   gt    0         console log fileNameAndLineNumber       else if navigator userAgent indexOf  Chrome      -1             var originFile   newErr stack split   n   1  split             var fileName   originFile originFile length - 1  split      0         var lineNumber   originFile originFile length - 1  split      1         console log fileName   line   lineNumber

User · Answer

Line number is actually something static  so if you just want it for logging then it could be preprocessed with something like gulp  I ve written a small gulp plugin that does exactly that   var gulp   require  gulp    var logLine   require  gulp-log-line    gulp task  log-line   function         return gulp src  file js    buffer   true         Write here the loggers you use           pipe logLine   console log              pipe gulp dest    build         gulp task  default     log-line      This will attach the file name and line to all logs from console log  so console log something  will become console log  filePath fileNumber   something   The advantage is that now you can concat your files  transpile them    and you will still get the line

User · Answer

console log new Error     It will show you the whole track

User · Answer

kangax s solution introduces unnecessary try  catch scope  If you need to access the line number of something in JavaScript  as long as you are using Firefox or Opera   just access  new Error  lineNumber

User · Answer

Answers are simple   No and No  No    By the time javascript is running the concept of source files urls from which the come is gone     There is also no way to determine a line number because again by the time of execution the notion of code  lines  is no longer meaningful in Javascript   Specific implementations may provide API hooks to allow priviledged code access to such details for the purpose of debugging but these APIs are not exposed to ordinary standard Javascript code

User · Answer

This works for me in chrome QtWebView  function getErrorObject        try   throw Error       catch err    return err       var err   getErrorObject    var caller line   err stack split   n   4   var index   caller line indexOf  at     var clean   caller line slice index 2  caller line length

User · Answer

Here is what I wrote based on info found on this forum   This is part of a MyDebugNamespace  Debug is apparently reserved and won t do as namespace name       var DEBUG   true             if  true    DEBUG  amp  amp   test                var sAlert    Assertion failed             if  null    message              sAlert      n    message          if  null    err              sAlert      n     File      err fileName     n     Line      err lineNumber          alert sAlert                How to call       MyDebugNamespace Assert new Error       null    someVar    Something is wrong      I included two functions with variable number of arguments calling this base code in my namespace so as to optionally omit message or error in calls   This works fine with Firefox  IE6 and Chrome report the fileName and lineNumber as undefined

User · Answer

the following code works for me in Mozilla and Chrome   Its log function that shows the file s name and the line of the caller   log  function  arg        var toPrint           for  var i   0  i  lt  arguments length    i            toPrint push arguments i               function getErrorObject            try   throw Error       catch err    return err               var err   getErrorObject            caller       if    browser mozilla            caller   err stack split   n   2         else           caller   err stack split   n   4              var index   caller indexOf   js         var str   caller substr 0  index   3       index   str lastIndexOf           str   str substr index   1  str length        var info     t tFile      str       if    browser mozilla            str   caller        else           index   caller lastIndexOf               str   caller substr 0  index             index   str lastIndexOf           str   str substr index   1  str length       info      Line      str      toPrint push info        console log apply console  toPrint

User · Answer

I realize this is an old question but there is now a method called console trace  Message   that will show you the line number and the chain of method calls that led to the log along with the message you pass it  More info on javascript logging tricks are available here at freecodecamp and this medium blog post

User · Answer

If you would like to know the line number for debugging purposes  or only during development  For a reason or another   you could use Firebug  a Firefox extension  and throw an exception   Edit   If you really need to do that in production for some reason  you can pre-process your javascript files in order for each function to keep track of the line it is on  I know some frameworks that find the coverage of code use this  such as JSCoverage    For example  let s say your original call is   function x       1   1    2   2    y        You could write a preprocessor to make it into   function x       var me   arguments callee    me line   1    1   1    me line   2    2   2    me line   3    y        Then in y    you could use arguments callee caller line to know the line from which it was called  such as   function y       alert arguments callee caller line

User · Answer

It seems I m kind of late     but the discussion is pretty interesting so   here it goes    Assuming you want to build a error handler   and you re using your own exception handler class like   function  errorHandler error       this errorMessage   error    errorHandler prototype  displayErrors   function        throw new Error this errorMessage       And you re wrapping your code like this   try  if condition         whatever     else      throw new errorHandler  Some Error Message       catch e       e displayErrors        Most probably you ll have the error handler in a separate  js file   You ll notice that in firefox or chrome s error console the code line number and file name  showed is the line file  that throws the  Error  exception and not the  errorHandler  exception wich you really want in order to make debugging easy  Throwing your own exceptions is great but on large projects locating them can be quite an issue  especially if they have similar messages   So  what you can do is to pass a reference to an actual empty Error object to your error handler  and that reference will hold all the information you want  for example in firefox you can get the file name  and line number etc     in chrome you get something similar if you read the  stack  property of the Error instance   Long story short   you can do something like this   function  errorHandler error  errorInstance       this errorMessage   error      this  errorInstance   errorInstance    errorHandler prototype  displayErrors   function          add the empty error trace to your message     this errorMessage       stack trace     this  errorInstance stack      throw new Error this errorMessage      try  if condition         whatever     else      throw new errorHandler  Some Error Message   new Error        catch e       e displayErrors        Now you can get the actual file and line number that throwed you custom exception

[javascript] How to get JavaScript caller function line number? How to get JavaScript caller source URL?

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