Vue: how to make textarea didn't change line ...

There are several things wrong with your example:

Instead of @keyup.onEnter="update", you have to call @keyup.enter="onEnter", because the name of your method is onEnter, not update, and the name of the modifier is enter, not onEnter.

Second: The newline is put into the textarea on keydown, not on keyup, so the complete code should be:

<div id="editor">
  <textarea :value="input" @keydown.enter="onEnter"></textarea>
</div>

Here is an updated fiddle: https://jsfiddle.net/tedt89kv/

Also, keep in mind that your users may Copy and Paste text with newlines into your document. Maybe a Watcher would be more what you want. In the watcher, you could remove all newlines on every change of the textarea's value.

Also, from the issue template that you removed to post your question:

The issue list of this repo is exclusively for bug reports and feature requests. For simple questions, please use the following resources:

• Read the docs: https://vuejs.org/guide/
• Watch video tutorials: https://laracasts.com/series/learning-vue-step-by-step
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thank u ... i will think more next time