jsclass

Console

Most JavaScript environments have some sort of console that allows running programs to print output, log messages and the like. In web browsers, this capability is provided by the console object, and in server-side environments the program may write output to the terminal. Console provides a single interface to all these facilities, using the most appropriate device wherever it is being used.

// In the browser
JS.require('JS.Console', function(Console) { ... });

// In CommonJS
var Console = require('jsclass/src/console').Console;

When writing output to a terminal, or the WebKit developer console, Console also supports many formatting commands for changing the color and other attributes of printed text.

The main two output methods are as follows:

• Console.puts(string) – prints string to the console with a line break afterward, so that subsequent messages appear on the next line.
• Console.print(string) – prints string without applying line breaks, allowing multiple print() calls to write output to the same line if the console supports this. In environments that don’t support this, the output is buffered until the next puts() call.

The output devices used are as follows:

• In web browsers that support window.console, the development console is used to log output.
• In web browsers with no console object, the alert() function is used.
• In Adobe AIR applications running under adl, the runtime.trace() function is used to write to the terminal.
• In programs running in a terminal, output is sent to stdout.

Formatting

The following formatting commands are available for formatting output. Not all environments support formatting, and on those environments these commands will be ignored. All commands are methods of Console, for example you can switch to bold text by calling Console.bold(). Text printed after the command has been issued will have the formatting applied to it. In environments that do not support formatting these methods have no effect.

• reset() resets all formatting attributes
• bold(), normal() set the weight of the text
• italic(), noitalic() switch between italic and roman text
• underline(), noline() apply and remove underlining
• blink(), noblink() apply and remove blinking text
• black(), red(), green(), yellow(), blue(), magenta(), cyan(), white(), nocolor() set the current text color
• Color methods can be prefixed with bg, for example bgyellow(), to set the current background color

Multiple formatting instructions can be combined using this method:

Console.consoleFormat('bold', 'red');

The consoleFormat() method takes a list of formatting instructions as input. It calls reset() and then applies the given formats.

On some platforms, Console also supports a set of commands for moving the cursor and clearing parts of the screen, for creating interfaces in the terminal. Those commands are:

• cursorUp(n), cursorDown(n), cursorForward(n), cursorBack(n) move the cursor n places in the given direction
• cursorNextLine(n), cursorPrevLine(n) move the cursor by n lines
• cursorColumn(x) moves the cursor to column x
• cursorPosition(x,y) moves the cursor to column x, row y
• cursorHide(), cursorShow() hides and shows the cursor
• eraseScreen() clears the entire terminal screen
• eraseScreenForward(), eraseScreenBack() clears everything either after or before the cursor position
• eraseLine() clears the whole of the current line
• eraseLineForward(), eraseLineBack() clears the current line either to the right or the left of the cursor

Console as a mixin

Finally note that Console can be used as a mixin so all the above methods appear in the current class:

Logger = new Class({
    include: Console,

    info: function(message) {
        this.bgblack();
        this.white();
        this.print('INFO');
        this.reset();
        this.puts(' ' + message);
    }
});