Related
Reference:
Using the new code snippets feature in google chrome
I am using the code snippets in google chrome, so say I have a snippet file.
check_consistency.js
Is there an api or a global object through which we can run the snippet directly from the command line, something like:
window.runSnippet('check_consistency.js')
or maybe call methods defined in the snippet directly.
Workflow Tip 1
I also want to see this functionality added. Meanwhile, perhaps try opening the Sources where (as you know) you can select a snippet and right click it to run it. You may or may not know that you can tap Esc on this page in order to show the console at the same time as your snippets:
Workflow Tip 2
The snippets documentation also mentions
The ability to quickly locate a specific file can be essential to a developer's workflow. The DevTools allow you to search across all script, stylesheet and snippet files using the following shortcuts:
Ctrl + O (Windows, Linux)
Cmd + O (Mac OSX)
which will work regardless of the panel you are currently in.
...and...
A keyboard shortcut is also available for easily executing a snippet - just select your snippet then use Ctrl/Cmd + Enter to run it. This replicates the behavior of the Run (>) button - currently in the Sources console, but which will be moving into the debugger control in the near future.
What this means is that while in the console you can press Ctrl/Cmd+O to quickly select your snippet, and then press Cmd/Control+Enter to run it.
I have a work around for when I'm running snippets a bunch of times on a site. I wrap my snippet code in a function and assign it to a global variable.
e.g.,
window.mySnippet = function (value) {
console.log(value.toUpperCase());
};
When I run this snippet I can now run
mySnippet('hello world');
-> "HELLO WORLD"
You still have to run the snippet once to load it into memory, but it's better than nothing.
I am a chronic user of Firebug, and I frequently need to log various stuff so that I can see what I am doing. The console.log function is a lot to type. Even if I assign it to a single letter variable like q = console.log, I have to do it every time I fire up Firebug. Is there any way to do it such that q always refer to console.log (unless, of course, I override it in my session)?
To answer your question, the functionality doesn't currently exist, however I have found the firebug developers to be very responsive in the past. Why don't you put in a feature request on their forum, or better yet, code it up yourself, and ask them to add it?
Depending on your IDE, simply setup a code snippet (I use Flash Develop, so Tools -> Code Snippets).
I believe this to be a better way than setting up redirect scripts and what not, because it stops the Firebug namespace from being polluted, and makes it easier/more consistent to debug if your debugging breaks down.
The screenshot shows me using Flash Develop, hitting Ctrl+B, then hit enter. The pipe (|) in the snippet indicates where the cursor will be placed to start typing after inserting the snippet.
What is the use of console.log?
Please explain how to use it in JavaScript, with a code example.
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 && window.console.log) {
// console is available
}
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.
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.
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!
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(){} }; }
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.
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 && console.log) {
console.log(this);
}
return this;
}
which you can then invoke like
$('foo.bar').find(':baz').log().hide();
to easily check inside jQuery chains.
console.log has nothing to do with jQuery.
It logs a message to a debugging console, such as Firebug.
A point of confusion sometimes is that to log a text message along with the contents of one of your objects using console.log, you have to pass each one of the two as a different argument. This means that you have to separate them by commas because if you were to use the + operator to concatenate the outputs, this would implicitly call the .toString() method of your object. This in most cases is not explicitly overriden and the default implementation inherited by Object doesn't provide any useful information.
Example to try in console:
>>> var myObj = {foo: 'bar'}
undefined
>>> console.log('myObj is: ', myObj);
myObj is: Object { foo= "bar"}
whereas if you tried to concatenate the informative text message along with the object's contents you'd get:
>>> console.log('myObj is: ' + myObj);
myObj is: [object Object]
So keep in mind that console.log in fact takes as many arguments as you like.
Use console.log to add debugging information to your page.
Many people use alert(hasNinjas) for this purpose but console.log(hasNinjas) is easier to work with. Using an alert pop-ups up a modal dialog box that blocks the user interface.
Edit: I agree with Baptiste Pernet and Jan Hančič that it is a very good idea to check if window.console is defined first so that your code doesn't break if there is no console available.
An example - suppose you want to know which line of code you were able to run your program (before it broke!), simply type in
console.log("You made it to line 26. But then something went very, very wrong.")
You use it to debug JavaScript code with either Firebug for Firefox, or JavaScript console in WebKit browsers.
var variable;
console.log(variable);
It will display the contents of the variable, even if it is a array or object.
It is similar to print_r($var); for PHP.
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
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.
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
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.
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.
It is used to log (anything you pass it) to the Firebug console. The main usage would be to debug your JavaScript code.
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.
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.
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.
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);
I try to explain in easy way:
Why Useable:
The console.log() method writes a message to the console and display it.
~very useful for testing purposes.
~Use them under/inside script tags.
How To See:
=>Press F12
Syntax:
console.log(message you want to display);
~Accepts a parameter and display it.
Working With Array:
var myArray = ["Ali", "John", "Shahrukh"];
console.log(myArray);
Working With Objects:
var myObject = { firstname : "Ali", lastname : "Rana" };
console.log(myObject);
Working With Text:[method 1]:
console.log("Hello StackOverflow");
Working With Text:[method 2]
var str = "Hello StackOverflow";
console.log(str);
Working With Numbers:
var myvar = '2';
console.log(myvar);
Working With Function:
function myfunction() { return (5 * 19); }
console.log(function());
Display Message With Argument:
var a = 2;
console.log("The value of a is " + a);
Hope, It May Helps.
The console.log() is a function in JavaScript which is used to print any kind of variables defined before in it or to just print any message that needs to be displayed to the user.
EG CODE:
function func() { return (5 * 18); }
console.log(func());
IMG:
OUTPUT:
console.log() : This method is well known and most common which can output anything of any type. Pass string, number, object or even html elements as a parameter and it will print same for you.
Ex.
console.log('Your print statements here!');
console.log('2nd parameter is type object', {type: 'object'});
console.log('can print with multiple parameters', 100001, {type: 'object'});
Find more about console with examples from here: console
console.log() is for a developer to generally logging output information.
You also have other console methods as shown below
console.assert()
//Log a message and stack trace to console if the first argument is false.
console.clear()
// Clear the console.
console.count()
// Log the number of times this line has been called with the given label.
console.countReset()
// Resets the value of the counter with the given label.
console.debug()
// Outputs a message to the console with the log level debug.
console.dir()
// Displays an interactive listing of the properties of a specified JavaScript object. This listing lets you use disclosure triangles to examine the contents of child objects.
console.dirxml()
// Displays an XML/HTML Element representation of the specified object if possible or the JavaScript Object view if it is not possible.
console.error()
// Outputs an error message. You may use string substitution and additional arguments with this method.
console.exception()
// Non-Standard
// An alias for error().
console.group()
// Creates a new inline group, indenting all following output by another level. To move back out a level, call groupEnd().
console.groupCollapsed()
// Creates a new inline group, indenting all following output by another level. However, unlike group() this starts with the inline group collapsed requiring the use of a disclosure button to expand it. To move back out a level, call groupEnd().
console.groupEnd()
// Exits the current inline group.
console.info()
// Informative logging of information. You may use string substitution and additional arguments with this method.
console.log()
// For general output of logging information. You may use string substitution and additional arguments with this method.
console.profile()
// Non-Standard
// Starts the browser's built-in profiler (for example, the Firefox performance tool). You can specify an optional name for the profile.
console.profileEnd()
// Non-Standard
// Stops the profiler. You can see the resulting profile in the browser's performance tool (for example, the Firefox performance tool).
console.table()
// Displays tabular data as a table.
console.time()
// Starts a timer with a name specified as an input parameter. Up to 10,000 simultaneous timers can run on a given page.
console.timeEnd()
// Stops the specified timer and logs the elapsed time in milliseconds since it started.
console.timeLog()
// Logs the value of the specified timer to the console.
console.timeStamp()
// Non-Standard
// Adds a marker to the browser's Timeline or Waterfall tool.
console.trace()
// Outputs a stack trace.
console.warn()
What is the use of console.log?
Please explain how to use it in JavaScript, with a code example.
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 && window.console.log) {
// console is available
}
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.
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.
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!
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(){} }; }
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.
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 && console.log) {
console.log(this);
}
return this;
}
which you can then invoke like
$('foo.bar').find(':baz').log().hide();
to easily check inside jQuery chains.
console.log has nothing to do with jQuery.
It logs a message to a debugging console, such as Firebug.
A point of confusion sometimes is that to log a text message along with the contents of one of your objects using console.log, you have to pass each one of the two as a different argument. This means that you have to separate them by commas because if you were to use the + operator to concatenate the outputs, this would implicitly call the .toString() method of your object. This in most cases is not explicitly overriden and the default implementation inherited by Object doesn't provide any useful information.
Example to try in console:
>>> var myObj = {foo: 'bar'}
undefined
>>> console.log('myObj is: ', myObj);
myObj is: Object { foo= "bar"}
whereas if you tried to concatenate the informative text message along with the object's contents you'd get:
>>> console.log('myObj is: ' + myObj);
myObj is: [object Object]
So keep in mind that console.log in fact takes as many arguments as you like.
Use console.log to add debugging information to your page.
Many people use alert(hasNinjas) for this purpose but console.log(hasNinjas) is easier to work with. Using an alert pop-ups up a modal dialog box that blocks the user interface.
Edit: I agree with Baptiste Pernet and Jan Hančič that it is a very good idea to check if window.console is defined first so that your code doesn't break if there is no console available.
An example - suppose you want to know which line of code you were able to run your program (before it broke!), simply type in
console.log("You made it to line 26. But then something went very, very wrong.")
You use it to debug JavaScript code with either Firebug for Firefox, or JavaScript console in WebKit browsers.
var variable;
console.log(variable);
It will display the contents of the variable, even if it is a array or object.
It is similar to print_r($var); for PHP.
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
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.
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
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.
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.
It is used to log (anything you pass it) to the Firebug console. The main usage would be to debug your JavaScript code.
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.
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.
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.
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);
I try to explain in easy way:
Why Useable:
The console.log() method writes a message to the console and display it.
~very useful for testing purposes.
~Use them under/inside script tags.
How To See:
=>Press F12
Syntax:
console.log(message you want to display);
~Accepts a parameter and display it.
Working With Array:
var myArray = ["Ali", "John", "Shahrukh"];
console.log(myArray);
Working With Objects:
var myObject = { firstname : "Ali", lastname : "Rana" };
console.log(myObject);
Working With Text:[method 1]:
console.log("Hello StackOverflow");
Working With Text:[method 2]
var str = "Hello StackOverflow";
console.log(str);
Working With Numbers:
var myvar = '2';
console.log(myvar);
Working With Function:
function myfunction() { return (5 * 19); }
console.log(function());
Display Message With Argument:
var a = 2;
console.log("The value of a is " + a);
Hope, It May Helps.
The console.log() is a function in JavaScript which is used to print any kind of variables defined before in it or to just print any message that needs to be displayed to the user.
EG CODE:
function func() { return (5 * 18); }
console.log(func());
IMG:
OUTPUT:
console.log() : This method is well known and most common which can output anything of any type. Pass string, number, object or even html elements as a parameter and it will print same for you.
Ex.
console.log('Your print statements here!');
console.log('2nd parameter is type object', {type: 'object'});
console.log('can print with multiple parameters', 100001, {type: 'object'});
Find more about console with examples from here: console
console.log() is for a developer to generally logging output information.
You also have other console methods as shown below
console.assert()
//Log a message and stack trace to console if the first argument is false.
console.clear()
// Clear the console.
console.count()
// Log the number of times this line has been called with the given label.
console.countReset()
// Resets the value of the counter with the given label.
console.debug()
// Outputs a message to the console with the log level debug.
console.dir()
// Displays an interactive listing of the properties of a specified JavaScript object. This listing lets you use disclosure triangles to examine the contents of child objects.
console.dirxml()
// Displays an XML/HTML Element representation of the specified object if possible or the JavaScript Object view if it is not possible.
console.error()
// Outputs an error message. You may use string substitution and additional arguments with this method.
console.exception()
// Non-Standard
// An alias for error().
console.group()
// Creates a new inline group, indenting all following output by another level. To move back out a level, call groupEnd().
console.groupCollapsed()
// Creates a new inline group, indenting all following output by another level. However, unlike group() this starts with the inline group collapsed requiring the use of a disclosure button to expand it. To move back out a level, call groupEnd().
console.groupEnd()
// Exits the current inline group.
console.info()
// Informative logging of information. You may use string substitution and additional arguments with this method.
console.log()
// For general output of logging information. You may use string substitution and additional arguments with this method.
console.profile()
// Non-Standard
// Starts the browser's built-in profiler (for example, the Firefox performance tool). You can specify an optional name for the profile.
console.profileEnd()
// Non-Standard
// Stops the profiler. You can see the resulting profile in the browser's performance tool (for example, the Firefox performance tool).
console.table()
// Displays tabular data as a table.
console.time()
// Starts a timer with a name specified as an input parameter. Up to 10,000 simultaneous timers can run on a given page.
console.timeEnd()
// Stops the specified timer and logs the elapsed time in milliseconds since it started.
console.timeLog()
// Logs the value of the specified timer to the console.
console.timeStamp()
// Non-Standard
// Adds a marker to the browser's Timeline or Waterfall tool.
console.trace()
// Outputs a stack trace.
console.warn()
How to Debug java Script Error Using Firebug?
Duplicate
How can I set breakpoints in an external JS script in Firebug
Debug using FireBug.
Just check the line on which the error is occuring, then, just before that line, write a "debugger" call.
debugger; //Will invoke FireBug's debugger.
var err = abcs; //Line containing error
To debug an error in firebug :
1- select inspect tab from menu
2- Set break point in the line that
causes error
3- Refrsh the page
4- use F10 to step by step debug and
F5 to end debgging
It's like debgging of visual studio
Use the console.log(yourObject) function to output anything to the firebug console. It is just like running a var_dump and you can view all your objects and their contents. This is very helpful if you want to check on the contents of a particular variable or even a particular DOM object.
Instead of using cheap alerts - the console.log() function is cleaner and you can see all the outputs neatly in your console pane.
Note however you need to remove all references to the console.log function when you deploy your website as it would not run in IE.
you can put breakpoints in the code, and wait for the execution to hit them. Then you can walk in the code, and use watches to know the values of variables.
You can use Firebug, and for debugging in chrome, you can use firebug lite
Why Firebug , try Visual studio , it has a rich debugging features ;)