How to Keep a Scrollable Chat Div Stuck to the Bottom When the Outer Container Resizes?

Scrollable div to stick to bottom, when outer div changes in size

Problem:

In a chat application interface, a scrollable div containing messages should stick to the bottom of the outer div, even if the outer div changes in size. For example, when the user adjusts the size of the text input area, the message div should remain at the bottom.

Solution:

1. CSS Approach:

Use flex-direction: column-reverse; for the outer div. This reverses the order of elements in the flex container, effectively placing the message div at the bottom.

.outer-div {
  display: flex;
  flex-direction: column-reverse;
}

.message-div {
  flex: 1;
  overflow-y: scroll;
}

2. JavaScript Approach:

If the CSS solution is incompatible with certain browsers, you can use JavaScript to handle the resizing and repositioning of the message div:

// Resize function to adjust message div height
function resizeMessageDiv() {
  const messageDiv = document.querySelector('.message-div');
  messageDiv.style.height = calcMessageDivHeight();
}

// Helper function to calculate the message div height
function calcMessageDivHeight() {
  const outerDiv = document.querySelector('.outer-div');
  return outerDiv.clientHeight - document.querySelector('.text-input').clientHeight;
}

// Event listener for text input changes
document.querySelector('.text-input').addEventListener('input', resizeMessageDiv);

window.addEventListener('load', resizeMessageDiv); // Initial resize on page load

Additional Note:

While the JavaScript solution is more flexible and handles browser compatibility better, it requires keeping track of events and manually updating the message div's height, which can introduce performance overhead and be less efficient than the CSS approach in certain scenarios.

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