JavaScript Console commands

Applies to Windows and Windows Phone](../Image/windows_and_phone_content.png "windows_and_phone_content")

You can use commands to send messages and perform other tasks in the JavaScript Console window of Visual Studio. For examples that show how to use that window, see QuickStart: Debug JavaScript. The information in this topic applies to Windows Store apps, Windows Phone Store apps, and apps created using Visual Studio Tools for Apache Cordova. For info on supported console commands in Cordova apps, see Debug Your App. For info on using the console in Internet Explorer F12 tools, see this topic.

If the JavaScript Console window is closed, you can open it while you're debugging in Visual Studio by choosing Debug > Windows > JavaScript Console.

console object commands

This table shows the syntax for the console object commands that you can use in the JavaScript Console window, or that you can use to send messages to the console from your code. This object provides a number of forms so that you can distinguish between informational messages and error messages, if you want to.

You can use the longer command form window.console.[command] if you need to avoid possible confusion with local objects named console.

Miscellaneous commands

These commands are also available in the JavaScript Console window (they are not available from code).

Checking whether a console command exists

You can check whether a specific command exists before attempting to use it. This example checks for the existence of the console.log command. If console.log exists, the code calls it.

if (console && console.log) {  
    console.log("msg");  
}  
  

Examining objects in the JavaScript Console window

You can interact with any object that's in scope when you use the JavaScript Console window. To inspect an out-of-scope object in the console window, use console.log , console.dir, or other commands from your code. Alternatively, you can interact with the object from the console window while it is in scope by setting a breakpoint in your code (Breakpoint > Insert Breakpoint).

Formatting console.log output

If you pass multiple arguments to console.log, the console will treat the arguments as an array and concatenate the output.

var user = new Object();  
user.first = "Fred";  
user.last = "Smith";  
  
console.log(user.first, user.last);  
// Output:  
// Fred Smith  
  

console.log also supports "printf" substitution patterns to format output. If you use substitution patterns in the first argument, additional arguments will be used to replace the specified patterns in the order they are used.

The following substitution patterns are supported:

• %s - string
  %i - integer
  %d - integer
  %f - float
  %o - object
  %b - binary
  %x - hexadecimal
  %e - exponent

  Here are some examples of using substitution patterns in console.log:

var user = new Object();  
user.first = "Fred";  
user.last = "Smith";  
user.age = 10.01;  
console.log("Hi, %s %s!", user.first, user.last);  
console.log("%s is %i years old!", user.first, user.age);  
console.log("%s is %f years old!", user.first, user.age);  
  
// Output:  
// Hi, Fred Smith!  
// Fred is 10 years old!  
// Fred is 10.01 years old!  

See Also

QuickStart: Debug JavaScript
Quickstart: Debug HTML and CSS