suppressCompleteMessage Method
As of Q1 2015, the suppressCompleteMessage property of the OnClientCheckFinished event's arguments is a method.
To prevent the informational alert, you now have to pass false as an argument(Example 1), instead of setting the property value, as in older versions (Example 2).
function OnClientCheckFinishedHandler(sender, args) {
args.suppressCompleteMessage(true);//prevent the alert
console.log('Spell check is complete');
}
function OnClientCheckFinishedHandler(sender, args) {
args.suppressCompleteMessage = true;//prevent the alert
console.log('Spell check is complete');
}