Is there a way to print a console message with Flutter?

I'm debugging an app, but I need to know some values in the fly, I was wondering if there's a way to print a message in console like console.log using Javascript.

I appreciate the help.

print() is probably what you are looking for. Here's some more info on debugging in flutter.

You can use

print() 

function or

debugPrint()

The debugPrint() function can print large outputs.

There are more helpful methods in import 'dart:developer' library and one of them is log().

example:

int i = 5;
log("Index number is: $i");

//output
[log] Index number is: 5

> void log(String message, {DateTime time, int sequenceNumber, int level > = 0, String name = '', Zone zone, Object error, StackTrace stackTrace}) > > Emit a log event. > > This function was designed to map closely to the logging information > collected by package:logging. > > [message] is the log message > [time] (optional) is the timestamp > [sequenceNumber] (optional) is a monotonically increasing sequence number > [level] (optional) is the severity level (a value between 0 and 2000); see the package:logging Level class for an overview of the > possible values > [name] (optional) is the name of the source of the log message > [zone] (optional) the zone where the log was emitted > [error] (optional) an error object associated with this log event > [stackTrace] (optional) a stack trace associated with this log event

Read more.:

print() is from dart:core and its implementation:

/// Prints a string representation of the object to the console.
void print(Object object) {
  String line = "$object";
  if (printToZone == null) {
    printToConsole(line);
  } else {
    printToZone(line);
  }
}

debugPrint():

/// Prints a message to the console, which you can access using the "flutter"
/// tool's "logs" command ("flutter logs").
///
/// If a wrapWidth is provided, each line of the message is word-wrapped to that
/// width. (Lines may be separated by newline characters, as in '\n'.)
///
/// By default, this function very crudely attempts to throttle the rate at
/// which messages are sent to avoid data loss on Android. This means that
/// interleaving calls to this function (directly or indirectly via, e.g.,
/// [debugDumpRenderTree] or [debugDumpApp]) and to the Dart [print] method can
/// result in out-of-order messages in the logs

// read more here: https://api.flutter.dev/flutter/foundation/debugPrint.html
DebugPrintCallback debugPrint = debugPrintThrottled;


/// Alternative implementation of [debugPrint] that does not throttle.
/// Used by tests. 
debugPrintSynchronously(String message, { int wrapWidth })

/// Implementation of [debugPrint] that throttles messages. This avoids dropping
/// messages on platforms that rate-limit their logging (for example, Android).
void debugPrintThrottled(String message, { int wrapWidth })

Read more.

Note that only the print() is taking any type and print to the console. debugPrint() and log() only take String. So, you have to add .toString() or use string interpolation like I shown in provided example snippet.

I tend to do something similar to this

Foo foo;
try{
    foo = _someMethod(); //some method that returns a new object
} catch (e) {
    print('_someMethod: Foo Error ${foo.id} Error:{e.toString()}'); /*my custom error print message. You don't need brackets if you are printing a string variable.*/
}

Use debug print to avoid logging in production application.

debugPrint("Message");

You can also disable or change debug print implementation in main.dart or any other file like this:

debugPrint = (String message, {int wrapWidth}) 
{
    debugPrintThrottled(message);//Or another other custom code
};

print, debugPrint and others have got some word limit restrictions, if you have something long to print on console, you can:

Create this method:

void printWrapped(String text) {
  final pattern = RegExp('.{1,800}'); // 800 is the size of each chunk
  pattern.allMatches(text).forEach((match) => print(match.group(0)));
}

Usage:

printWrapped("Your very long string ...");

Source

One more answer for Concatenate with String:

// Declaration
int number = 10;


//Button Action
RaisedButton(
child: Text("Subtract Me"),
onPressed: () {
      number = number - 1;
      print('You have got $number as result');
      print('Before Value is ${number - 1} and After value is ${number + 1}');
    },
),

//Output:
flutter: You have got 9 as result
flutter: Before Value is 8 and After value is 10

I think this might help you, because, I was also got stuck in many ways of knowing the output of my code in the dart file, hence I got the solution by following the steps, shown in the video.

https://www.youtube.com/watch?v=hhP1tE-IHos

here I have shown an instance of how it works after following the video. check the left side column where it shows about the value which profile variable carry i.e., null

debugPrint()

Might as well use rather than print() as it attempts to reduce log line drop or being out of order on Android kernel

Refs:

Logging in Flutter

you can simply use print('whatever you want to print') same as console.log() in javascript.

for more info you can check here.

Note that the print() and log() options both add their own labels at the start of the line, and apply additional formatting that can cause long lines to be truncated. In the case of a dart:io app, you can bypass this interception and mangling entirely by going directly to stdout/stderr, etc. as in stdout.write(), stdout.writeln(), etc. Likewise if you are looking to log explicitly to one or the other. I ran into this issue when adding CLI args to a flutter application.