The onerror event of the window object

The onerror event of the window object

Defining the onerror event with a function that returns a value of true at the very top of your page suppresses all scripting errors on the page .

window.onerror=function(){
 alert('An error has occurred!')
 return true
}

window.onerror=function(msg, url, linenumber){
 alert('Error message: '+msg+'\nURL: '+url+'\nLine Number: '+linenumber)
 return true
}

var errordialog=function(msg, url, linenumber){
    var dialog=document.createElement("div")
    dialog.className='errordialog'
    dialog.innerHTML=' JavaScript Error: ' + msg +' at line number ' + linenumber +'. Please inform webmaster.'
    document.body.appendChild(dialog)
    return true
}

window.onerror=function(msg, url, linenumber){
    return errordialog(msg, url, linenumber)
}