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By default, pressing the Enter key in a textarea element will create a new line. However, sometimes you may want to override this behavior and only insert new lines when Shift + Enter is pressed. This is useful in application where we use the Enter button to submit a form but also want to give users the ability to create new lines.

Preventing the Default Enter Behavior

To prevent the default Enter behavior, you can add a keydown event listener to the textarea element. In the listener, check if the Enter key was pressed without the Shift key. If so, call preventDefault() on the event to stop the default new line insertion.

Allowing Shift+Enter for New Lines

You likely still want to allow users to press Shift+Enter to create new lines. So in your keydown listener, check if both Enter and Shift were pressed together. If so, allow the default behavior of inserting a new line.

Example Code

HTML Code:

 <textarea id="myTextarea"></textarea>

JavaScript Code:

const textarea = document.getElementById('myTextarea');

textarea.addEventListener('keydown', (e) => {
  if(e.keyCode === 13 && !e.shiftKey) {
    e.preventDefault(); 
  }
}); 

Code Explanation:

• An event listener is added that will listen to any keydown event that occurs.
• Inside the handler, we change if the pressed key is ‘Enter‘ using e.keyCode, the Enter Key numeric key code is 13. And using e.shiftKey is used to check if the Shift key is held down. The e.shiftKey returns a Boolean value. It will be true if the Shift key is pressed.
• Using e.keyCode === 13 && !e.shiftKey we checked if the Enter button is pressed without the Shift key. If true, it will prevent the default new line insertion in the textarea.

This will prevent a new line on regular Enter, but allow it on Shift+Enter.

Usage Examples

Some examples of where you may want this behavior:

• Chat boxes – Send message on Enter, add line on Shift+Enter
• Inline editing – Save on Enter, new line on Shift+Enter
• Forms – Submit on Enter, new line on Shift+Enter

Summary

In summary, you can prevent the default textarea Enter behavior and only allow new lines when Shift + Enter is pressed. This is done by calling preventDefault() when Enter is pressed without Shift in a keydown listener. Useful for cases where you want Enter for another action like submitting a form.