Prevent line/paragraph breaks in contentEditable

You can attach an event handler to the keydown or keypress event for the contentEditable field and cancel the event if the keycode identifies itself as enter (or shift+enter).

This will disable enter/shift+enter completely when focus is in the contentEditable field.

If using jQuery, something like:

$("#idContentEditable").keypress(function(e){ return e.which != 13; });

...which will return false and cancel the keypress event on enter.

Add:

display: flex;

On the contenteditable html element

$("#idContentEditable").keypress(function(e){ return e.which != 13; });

Solution proposed by Kamens doesn't work in Opera, you should attach event to document instead.

/**
 * Pass false to enable
 */
var disableEnterKey = function(){
    var disabled = false;

    // Keypress event doesn't get fired when assigned to element in Opera
    $(document).keypress(function(e){
        if (disabled) return e.which != 13;
    });                 

    return function(flag){
        disabled = (flag !== undefined) ? flag : true;
    }
}();    

I came here searching for the same answer, and was surprised to find it's a rather simple solution, using the tried and true Event.preventDefault()

const input = document.getElementById('input');

input.addEventListener('keypress', (e) => {
  if (e.which === 13) e.preventDefault();
});

<div contenteditable="true" id="input">
  You can edit me, just click on me and start typing.
  However, you can't add any line breaks by pressing enter.
</div>

Use CSS:

word-break: break-all;

For me, its worked!