What is console log

Question

What is the use of console log    Please explain how to use it in JavaScript  with a code example

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Apart from the usages mentioned above  console log can also print to the terminal in node js  A server created with express  for eg   can use console log to write to the output logger file

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In early days JS debugging was performed through alert   function - now it is an obsolete practice     The console log   is a function that writes a message to log on the debugging console  such as  Webkit or Firebug  In a browser you will not see anything on the screen  It logs a message to a debugging console  It is only available in Firefox with  Firebug and in Webkit based browsers  Chrome and Safari   It does not work well in all IE releases   The console object is an extension to the DOM    The console log   should be used in code only during development and debugging   It   s considered bad practice that someone leaves console log   in the javascript file on the production server

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This is nothing to deal with the jQuery  The console log   is referencing to the console object s log function  which provides methods for logging information to the browser s console  These methods are intended for debugging purposes only and should not be relied on for presenting information to end users

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Quoting MDN Docs here  console     contains many methods that you can call to perform rudimentary debugging tasks  generally focused around logging various values to the browser s Web Console  By far the most commonly-used method is console log  which is used to log the current value contained inside a specific variable   How to use in Javascript  let myString    Hello World   console log myString    Also remember console is a part of global window object in the web browser  Thus the following is also technically correct but isn t used in practical scenario  let myString    Hello World   window console log myString

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An example - suppose you want to know which line of code you were able to run your program  before it broke    simply type in  console log  You made it to line 26  But then something went very  very wrong

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In java scripts there is no input and output functions  So to debug the code console log   method is used It is a method for logging  It will be printed under console log  development tools    Its is not present in IE8 and under until you open IE development tool

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It will post a log message to the browser s javascript console  e g  Firebug or Developer Tools  Chrome   Safari  and will show the line and file where it was executed from   Moreover  when you output a jQuery Object it will include a reference to that element in the DOM  and clicking it will go to that in the Elements HTML tab   You can use various methods  but beware that for it to work in Firefox  you must have Firebug open  otherwise the whole page will crash  Whether what you re logging is a variable  array  object or DOM element  it will give you a full breakdown including the prototype for the object as well  always interesting to have a poke around   You can also include as many arguments as you want  and they will be replaced by spaces   console log   myvar   Logged     console info  myvar   Logged     console warn  myvar   Logged     console debug myvar   Logged     console error myvar   Logged       These show up with different logos for each command   You can also use console profile profileName   to start profiling a function  script etc  And then end it with console profileEnd profileName   and it will show up in you Profiles tab in Chrome  don t know with FF    For a complete reference go to http   getfirebug com logging and I suggest you read it   Traces  groups  profiling  object inspection    Hope this helps

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I really feel web programming easy when i start console log for debugging   var i    If i want to check value of i runtime    console log i     you can check current value of i in firebug s console tab  It is specially used for debugging

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A point of confusion sometimes is that to log a text message along with the contents of one of your objects using console log  you have to pass each one of the two as a different argument  This means that you have to separate them by commas because if you were to use the   operator to concatenate the outputs  this would implicitly call the  toString   method of your object  This in most cases is not explicitly overriden and the default implementation inherited by Object doesn t provide any useful information   Example to try in console    gt  gt  gt  var myObj    foo   bar   undefined  gt  gt  gt  console log  myObj is     myObj   myObj is  Object   foo   bar     whereas if you tried to concatenate the informative text message along with the object s contents you d get    gt  gt  gt  console log  myObj is      myObj   myObj is   object Object    So keep in mind that console log in fact takes as many arguments as you like

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Places you can view the console  Just to have them all in one answer   Firefox  http   getfirebug com    you can also now use Firefox s built in developer tools Ctrl Shift J  Tools   Web Developer   Error Console   but Firebug is much better  use Firebug   Safari and Chrome  Basically the same   https   developers google com chrome-developer-tools docs overview  https   developer apple com technologies safari developer-tools html   Internet Explorer  Don t forget you can use compatibility modes to debug IE7 and IE8 in IE9 or IE10  http   msdn microsoft com en-us library ie gg589507 v vs 85  aspx  http   msdn microsoft com en-us library dd565628 v vs 85  aspx  If you must access the console in IE6 for IE7 use the Firebug Lite bookmarklet  http   getfirebug com firebuglite  look for stable bookmarklet   http   en wikipedia org wiki Bookmarklet  Opera  http   www opera com dragonfly   iOS  Works for all iPhones  iPod touch and iPads   http   developer apple com library ios ipad  DOCUMENTATION AppleApplications Reference SafariWebContent DebuggingSafarioniPhoneContent DebuggingSafarioniPhoneContent html  Now with iOS 6 you can view the console through Safari in OS X if you plug in your device  Or you can do so with the emulator  simply open a Safari browser window and go to the  Develop  tab  There you will find options to get the Safari inspector to communicate with your device   Windows Phone  Android  Both of these have no console built in and no bookmarklet ability  So we use  http   jsconsole com  type  listen and it will give you a script tag to place in your HTML  From then on you can view your console inside the jsconsole website   iOS and Android  You can also use http   html adobe com edge inspect  to access web inspector tools and the console on any device using their convenient browser plugin      Older browser problems  Lastly older versions of IE will crash if you use console log in your code and not have the developer tools open at the same time  Luckily it s an easy fix   Use the below code snippet at the top of your code    if  window console   window console    log  function             This checks to see if the console is present  and if not it sets it to an object with a blank function called log  This way window console and window console log is never truly undefined

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Beware  leaving calls to console in your production code will cause your site to break in Internet Explorer   Never keep it unwrapped   See  https   web archive org web 20150908041020 blog patspam com 2009 the-curse-of-consolelog

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There is nothing to do with jQuery and if you want to use it I advice you to do  if  window console        console log  your message       So you don t break your code when it is not available   As suggested in the comment  you can also execute that in one place and then use console log as normal  if   window console    window console     log  function

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console log has nothing to do with jQuery   It logs a message to a debugging console  such as Firebug

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It s not a jQuery feature but a feature for debugging purposes  You can for instance log something to the console when something happens  For instance       someButton   click function       console log   someButton was clicked         do something       You d then see  someButton was clicked in Firebug   s    Console    tab  or another tool   s console     e g  Chrome   s Web Inspector  when you would click the button   For some reasons  the console object could be unavailable  Then you could check if it is - this is useful as you don t have to remove your debugging code when you deploy to production   if  window console  amp  amp  window console log         console is available

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Use console log to add debugging information to your page    Many people use alert hasNinjas  for this purpose but console log hasNinjas  is easier to work with  Using an alert pop-ups up a modal dialog box that blocks the user interface   Edit  I agree with Baptiste Pernet and Jan Hancic that it is a very good idea to check if window console is defined first so that your code doesn t break if there is no console available

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console log has nothing to do with jQuery  It is a common object method provided by debuggers  including the Chrome debugger and Firebug  that allows a script to log data  or objects in most cases  to the JavaScript console

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If your browser supports debugging  you can use the console log   method to display JavaScript values   Activate debugging in your browser with F12  and select  Console  in the debugger menu   Console in JavaScript  Try to fix  or  debug   a non-functioning JavaScript program  and practice using the console log   command  There are shortcuts that is going to help you to access to the JavaScript console  based on the browser that you are using   Chrome Console Keyboard Shortcuts  Windows  Ctrl   Shift   J   Mac  Cmd   Option   J  Firefox Console Keyboard Shortcuts  Windows  Ctrl   Shift   K  Mac  Cmd   Option   K  Internet Explorer Console Keyboard Shortcuts  F12 key  Safari Console Keyboard Shortcuts  Cmd   Option   C

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console log specifically is a method for developers to write code to inconspicuously inform the developers what the code is doing  It can be used to alert you that there s an issue  but shouldn t take the place of an interactive debugger when it comes time to debug the code  Its asynchronous nature means that the logged values don t necessarily represent the value when the method was called   In short  log errors with console log  if available   then fix the errors using your debugger of choice  Firebug  WebKit Developer Tools  built-in to Safari and Chrome   IE Developer Tools or Visual Studio

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You use it to debug JavaScript code with either Firebug for Firefox  or JavaScript console in WebKit browsers   var variable   console log variable     It will display the contents of the variable  even if it is a array or object   It is similar to print r  var   for PHP

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It is used to log  anything you pass it  to the Firebug console  The main usage would be to debug your JavaScript code

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You can view any messages logged to the console if you use a tool such as Firebug to inspect your code  Let s say you do this   console log  Testing console      When you access the console in Firebug  or whichever tool you decide to use to inspect your code   you will see whatever message you told the function to log  This is particularly useful when you want to see if a function is executing  or if a variable is being passed assigned properly  It s actually rather valuable for figuring out just what went wrong with your code

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console log logs debug information to the console on some browsers  Firefox with Firebug installed  Chrome  IE8  anything with Firebug Lite installed   On Firefox it is a very powerful tool  allowing you to inspect objects or examine the layout or other properties of HTML elements  It isn t related to jQuery  but there are two things that are commonly done when using it with jQuery    install the FireQuery extension for Firebug  This  amongst other advantages  makes the logging of jQuery objects look nicer  create a wrapper that is more in line with jQuery s chaining code conventions    This means usually something like this     fn log   function         if  window console  amp  amp  console log            console log this             return this      which you can then invoke like     foo bar   find   baz   log   hide      to easily check inside jQuery chains

[javascript] What is console.log?

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