Why is console.log used? What does it do?

Question

I can see many place used console.log(). Can anyone tell me why it is used?

Something like this,

function createCheckBox( idsToShow ) {
    for( i = 0 ; i < 15 ; i++ ) {                
       console.log( idsToShow.indexOf('main' + i + '|' ) + '  ' + 'main' + i + '|' );
       if( idsToShow != '' && idsToShow.indexOf('main' + i + '|' ) == -1 ) continue;
       checkBoxs += "<li> <input type=\"checkbox\" id=\"main" +  i + "\" value=\"Example" + i + "\" name=\"lbl"+ i +"\" /> <label id=\"lbl"+ i +"\">Example" + i + "</label></li>";                                    
       ids += 'main' + i + '|'; //is the check box id.                     
    }
}

Answer 1

It logs things to a debug console (which is built into many browsers (e.g. Chrome Developer Tools) and available as an extension (e.g. Firebug for Firefox) in many others)

Answer 2

Everyone seems to use log, but console.info is more useful. In Firebug it gives you the line number where it came from, so you don't have to be so descriptive in the console message. It's also much easier to track down if a colleague leaves an errant console somewhere in your site.