2:nd revision of this answer
Your friend here is flex-direction: column-reverse; which does all you ask while align the messages at the bottom of the message container, just like for example Skype and many other chat apps do.
.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 }
.chat-input-text { width: 60%; min-height: 40px; max-width: 60%; }
The downside with flex-direction: column-reverse; is a bug in IE/Edge/Firefox, where the scrollbar doesn’t show, which your can read more about here: Flexbox column-reverse and overflow in Firefox/IE
The upside is you have ~ 90% browser support on mobile/tablets and ~ 65% for desktop, and counting as the bug gets fixed, …and there is a workaround.
// scroll to bottom
function updateScroll(el){
el.scrollTop = el.scrollHeight;
}
// only shift-up if at bottom
function scrollAtBottom(el){
return (el.scrollTop + 5 >= (el.scrollHeight - el.offsetHeight));
}
In the below code snippet I’ve added the 2 functions from above, to make IE/Edge/Firefox behave in the same way flex-direction: column-reverse; does.
function addContent () {
var msgdiv = document.getElementById('messages');
var msgtxt = document.getElementById('inputs');
var atbottom = scrollAtBottom(msgdiv);
if (msgtxt.value.length > 0) {
msgdiv.innerHTML += msgtxt.value + '<br/>';
msgtxt.value = "";
} else {
msgdiv.innerHTML += 'Long long content ' + (tempCounter++) + '!<br/>';
}
/* if at bottom and is IE/Edge/Firefox */
if (atbottom && (!isWebkit || isEdge)) {
updateScroll(msgdiv);
}
}
function resizeInput () {
var msgdiv = document.getElementById('messages');
var msgtxt = document.getElementById('inputs');
var atbottom = scrollAtBottom(msgdiv);
if (msgtxt.style.height == '120px') {
msgtxt.style.height="auto";
} else {
msgtxt.style.height="120px";
}
/* if at bottom and is IE/Edge/Firefox */
if (atbottom && (!isWebkit || isEdge)) {
updateScroll(msgdiv);
}
}
/* fix for IE/Edge/Firefox */
var isWebkit = ('WebkitAppearance' in document.documentElement.style);
var isEdge = ('-ms-accelerator' in document.documentElement.style);
var tempCounter = 6;
function updateScroll(el){
el.scrollTop = el.scrollHeight;
}
function scrollAtBottom(el){
return (el.scrollTop + 5 >= (el.scrollHeight - el.offsetHeight));
}html, body { height:100%; margin:0; padding:0; }
.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 }
.chat-input-text { width: 60%; min-height: 40px; max-width: 60%; }
/* temp. buttons for demo */
button { width: 12%; height: 44px; margin-left: 5%; vertical-align: top; }
/* begin - fix for hidden scrollbar in IE/Edge/Firefox */
.chat-messages-text{ overflow: auto; }
@media screen and (-webkit-min-device-pixel-ratio:0) {
.chat-messages-text{ overflow: visible; }
/* reset Edge as it identifies itself as webkit */
@supports (-ms-accelerator:true) { .chat-messages-text{ overflow: auto; } }
}
/* hide resize FF */
@-moz-document url-prefix() { .chat-input-text { resize: none } }
/* end - fix for hidden scrollbar in IE/Edge/Firefox */<div class="chat-window">
<div class="chat-messages">
<div class="chat-messages-text" id="messages">
Long long content 1!<br/>
Long long content 2!<br/>
Long long content 3!<br/>
Long long content 4!<br/>
Long long content 5!<br/>
</div>
</div>
<div class="chat-input">
<textarea class="chat-input-text" placeholder="Type your message here..." id="inputs"></textarea>
<button onclick="addContent();">Add msg</button>
<button onclick="resizeInput();">Resize input</button>
</div>
</div>Side note 1: The detection method is not fully tested, but it should work on newer browsers.
Side note 2: Attach a resize event handler for the chat-input might be more efficient then calling the updateScroll function.
Note: Credits to HaZardouS for reusing his html structure