How to Keep a Scrollable Chat Div at the Bottom When the Input Field Resizes?

Scrollable Div Sticking to Bottom When Outer Div Changes Size

Overview

In chat applications, it's common to have a scrollable message container that takes up most of the screen. However, when the input field dynamically increases in height, the user's scroll position can get disrupted.

The Problem

When the input field grows, it effectively increases the height of the outer div, which pushes the message container down. This causes the user to lose sight of recent messages.

React-based Solution

One approach is to use React's componentDidUpdate lifecycle method to calculate the input field's height and notify the message container if it changes. However, this can lead to performance issues and excessive message passing.

CSS Solution using Flexbox

A more efficient solution involves using CSS flexbox:

.chat-window {
  display: flex;
  flex-direction: column;
  height: 100%;
}

.chat-messages {
  flex: 1;
  height: 100%;
  overflow: auto;
  display: flex;
  flex-direction: column-reverse;
}

.chat-input {
  border-top: 1px solid #999;
  padding: 20px 5px;
}

• flex-direction: column-reverse; places the messages at the bottom of the container.
• This ensures that the messages remain in view even when the input field grows.

Considerations

• IE/Edge/Firefox Bug: These browsers exhibit a bug where the scrollbar can disappear when using flex-direction: column-reverse;.
• Workaround: To address this, add the following functions:

function updateScroll(el) {
  el.scrollTop = el.scrollHeight;
}

function scrollAtBottom(el) {
  return (el.scrollTop + 5 >= (el.scrollHeight - el.offsetHeight));
}

• Check if the container is at the bottom and adjust the scrollbar when the input field is resized in these browsers.

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