# Yahoo! UI Library

### yui 3.0.0

Yahoo! UI Library > yui > yui-log.js (source view)
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    /**
     * Provides console log capability and exposes a custom event for
     * console implementations.
     * @module yui
     * @submodule yui-log
     */
    (function() {

    var INSTANCE = Y,
        LOGEVENT = 'yui:log',
        UNDEFINED = 'undefined',
        LEVELS = { debug: 1, info: 1, warn: 1, error: 1 },
        _published;

    /**
     * If the 'debug' config is true, a 'yui:log' event will be
     * dispatched, which the Console widget and anything else
     * can consume.  If the 'useBrowserConsole' config is true, it will
     * write to the browser console if available.  YUI-specific log
     * messages will only be present in the -debug versions of the
     * JS files.  The build system is supposed to remove log statements
     * from the raw and minified versions of the files.
     *
     * @method log
     * @for YUI
     * @param  {String}  msg  The message to log.
     * @param  {String}  cat  The log category for the message.  Default
     *                        categories are "info", "warn", "error", time".
     *                        Custom categories can be used as well. (opt)
     * @param  {String}  src  The source of the the message (opt)
     * @param  {boolean} silent If true, the log event won't fire
     * @return {YUI}      YUI instance
     */
    INSTANCE.log = function(msg, cat, src, silent) {
        var Y = INSTANCE, c = Y.config, bail = false, excl, incl, m, f;
        // suppress log message if the config is off or the event stack
        // or the event call stack contains a consumer of the yui:log event
        if (c.debug) {
            // apply source filters
            if (src) {
                excl = c.logExclude;
                incl = c.logInclude;

                if (incl && !(src in incl)) {
                    bail = 1;
                } else if (excl && (src in excl)) {
                    bail = 1;
                }
            }

            if (!bail) {

                if (c.useBrowserConsole) {
                    m = (src) ? src + ': ' + msg : msg;
                    if (typeof console != UNDEFINED && console.log) {
                        f = (cat && console[cat] && (cat in LEVELS)) ? cat : 'log';
                        console[f](m);
                    } else if (typeof opera != UNDEFINED) {
                        opera.postError(m);
                    }
                }

                if (Y.fire && !silent) {
                    if (!_published) {
                        Y.publish(LOGEVENT, {
                            broadcast: 2,
                            emitFacade: 1
                        });

                        _published = 1;

                    }
                    Y.fire(LOGEVENT, {
                        msg: msg,
                        cat: cat,
                        src: src
                    });
                }
            }
        }

        return Y;
    };

    /**
     * Write a system message.  This message will be preserved in the
     * minified and raw versions of the YUI files, unlike log statements.
     * @method message
     * @for YUI
     * @param  {String}  msg  The message to log.
     * @param  {String}  cat  The log category for the message.  Default
     *                        categories are "info", "warn", "error", time".
     *                        Custom categories can be used as well. (opt)
     * @param  {String}  src  The source of the the message (opt)
     * @param  {boolean} silent If true, the log event won't fire
     * @return {YUI}      YUI instance
     */
    INSTANCE.message = function() {
        return INSTANCE.log.apply(INSTANCE, arguments);
    };

    })();

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