<script type="text/javascript">
function filtreAcc(c) {
switch (c){
case "é":
case "è":
return "e";
case "à":
return "a";
}
}
var txt = "jean-michel {é} {è} {à} du pont";
txt = txt.replace(/[éèà]/g, function(l){return filtreAcc(l)});
alert(txt);
</script>