JavaScript How do I print a message to the error console

Question

How can I print a message to the error console  preferably including a variable    For example  something like   print  x  d   x

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Visit https   developer chrome com devtools docs console-api for a complete console api reference      console error object Obj           In this case  object would be your error string

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This does not print to the Console  but will open you an alert Popup with your message which might be useful for some debugging   just do   alert  message

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The WebKit Web Inspector also supports Firebug s console API  just a minor addition to Dan s answer

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console error message     gives you the red errormessage console log message     gives the default message console warn message     gives the warn message with the exclamation mark in front of it console info message     gives an info message with an  i  in front of the message   You also can add CSS to your logging messages   console log   c My message here    background  blue  color  white  padding-left 10px

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As always  Internet nbsp Explorer is the big elephant in rollerskates that stops you just simply using console log     jQuery s log can be adapted quite easily  but is a pain having to add it everywhere  One solution if you re using jQuery is to put it into your jQuery file at the end  minified first   function log         if  arguments length  gt  0                   Join for graceful degregation         var args    arguments length  gt  1    Array prototype join call arguments         arguments 0               This is the standard  Firebug and newer WebKit browsers support this          try               console log args               return true            catch e                   Newer Opera browsers support posting erros to their consoles              try                   opera postError args                   return true                             catch e                                                     Catch all  a good old alert box          alert args           return false

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One good way to do this that works cross-browser is outlined in Debugging JavaScript  Throw Away Your Alerts

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The simplest way to do this is   console warn  Text to print on console

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A note about  throw    mentioned above  It seems that it stops execution of the page completely  I checked in IE8    so it s not very useful for logging  on going processes   like to track a certain variable      My suggestion is perhaps to add a textarea element somewhere in your document and to change  or append to  its value  which would change its text  for logging information whenever needed

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With es6 syntax you can use   console log  x     x

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x000D   x000D  function foo     x000D    function bar     x000D      console trace  Tracing is Done here    x000D      x000D    bar    x000D    x000D   x000D  foo    x000D   x000D   x000D     x000D   x000D  console log console     to print console object x000D  console clear  console clear      to clear console x000D  console log  console log      to print log message x000D  console info  console info      to print log message  x000D  console debug  console debug      to debug message x000D  console warn  console warn      to print Warning x000D  console error  console error      to print Error x000D  console table   car    fruits    color      to print data in table structure x000D  console assert  console assert      to print Error x000D  console dir   name   test      to print object x000D  console dirxml   name   test      to print object as xml formate x000D   x000D   x000D    To Print Error - console error  x  d   x      x000D   x000D  console log  This is the outer level    x000D  console group    x000D  console log  Level 2    x000D  console group    x000D  console log  Level 3    x000D  console warn  More of level 3    x000D  console groupEnd    x000D  console log  Back to level 2    x000D  console groupEnd    x000D  console log  Back to the outer level    x000D   x000D   x000D

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If you are using Firebug and need to support IE  Safari or Opera as well  Firebug Lite adds console log   support to these browsers

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To actually answer the question   console error  An error occurred     console error  An error occurred      My variable      myVar   console error  An error occurred       My variable       myVar     Instead of error  you can also use info  log or warn

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Here is a solution to the literal question of how to print a message to the browser s error console  not the debugger console    There might be good reasons to bypass the debugger    As I noted in comments about the suggestion to throw an error to get a message in the error console  one problem is that this will interrupt the thread of execution   If you don t want to interrupt the thread  you can throw the error in a separate thread  one created using setTimeout   Hence my solution  which turns out to be an elaboration of the one by Ivo Danihelka    var startTime    new Date    getTime    function logError msg      var milliseconds    new Date    getTime   - startTime    window setTimeout function          throw  new Error milliseconds          msg                 logError  testing      I include the time in milliseconds since the start time because the timeout could skew the order in which you might expect to see the messages     The second argument to the Error method is for the filename  which is an empty string here to prevent output of the useless filename and line number   It is possible to get the caller function but not in a simple browser independent way     It would be nice if we could display the message with a warning or message icon instead of the error icon  but I can t find a way to do that   Another problem with using throw is that it could be caught and thrown away by an enclosing try-catch  and putting the throw in a separate thread avoids that obstacle as well   However  there is yet another way the error could be caught  which is if the window onerror handler is replaced with one that does something different   Can t help you there

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If you use Safari  you can write  console log  your message here      and it appears right on the console of the browser

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Exceptions are logged into the JavaScript console  You can use that if you want to keep Firebug disabled   function log msg        setTimeout function             throw new Error msg          0       Usage   log  Hello World    log  another message

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console log  your message here      working for me   i m searching for this   i used Firefox  here is my Script       document   ready function     console log  all images are loaded          works in Firefox and Chrome

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Install Firebug and then you can use console log      and console debug       etc   see the documentation for more

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To answer your question you can use ES6 features   var var 10  console log  var   var

[javascript] JavaScript: How do I print a message to the error console?

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