check if input type="text" has a symbol

so i have regular input field.
how can i check if use inputs an apostrophe there?
so that if they do, i would alert("them") ?
i hope someone can help.
thanks.

if (/\'/g.test(thefieldName.value)) {
alert ("You have typed an apostrophe!")
}

if (/\'/g.test(thefieldName.value)) {
alert ("You have typed an apostrophe!")
}
Thank you so much!!! :thumbsup: