以下のコードで解決しました。
html
1<div id='body-text' class='body-text' contenteditable=true data-placeholder='Body Contents'></div>
javascript
1document.execCommand('defaultParagraphSeparator', false, 'p')
2
3var div = document.getElementById('body-text')
4div.addEventListener('keypress', onKeyPress)
5
6function onKeyPress(e) {
7 if (e.keyCode == '13') {
8 var text = div.firstChild.textContent
9 var len = text.length
10 var bgn = 0
11 var end = len
12 div.selectionStart = bgn
13 div.selectionEnd = end
14 document.execCommand('formatBlock', false, 'p')
15 div.removeEventListener('keypress', onKeyPress, false)
16 }
17}
18