Unable to detect “Enter key” in Javascript with Php

I am working with php and javascript, I have texarea and i want whenever i enter any text and
press “Enter key” then alert should display,But right now text is going to next line instead of display alert box,

Here is my html code

<textarea  placeholder="Write a comment1…" id="txt'.$FeedId.'" rows="1" class="reply_post_new" style="overflow:hidden" onkeypress="return Addcomment1(this)"></textarea>

And here is my script code,Where i am wrong ?

<script>
function Addcomment1(e) {
    f (e.keyCode == 13) {
        alert('Hello world');
        return false;
    }
}
</script>