Compartmentalize TextBox functionality

pico.css

     position: relative;
 }
 #textbox {
-    resize: vertical;
+    resize: none;
 }
 .post > div {
     display: inline;

pico.js

 const scrollIntoView = (vnode) => {
     vnode.dom.scrollIntoView()
 }
-const toggleFullscreen = (el) => (event) => {
-    const requestFullscreen = (el.requestFullscreen || el.webkitRequestFullscreen).bind(el)
-    document.fullscreenElement ? document.exitFullscreen() : requestFullscreen()
-}
-const prettyTime = (ts) => {
-    const dt = new Date(ts)
-    const H = `0${dt.getHours()}`.slice(-2)
-    const M = `0${dt.getMinutes()}`.slice(-2)
-    const S = `0${dt.getSeconds()}`.slice(-2)
-    return `${H}:${M}:${S}`
-}
-const blockIndent = (text, iStart, iEnd, nLevels) => {
-    // prop
-    const startLine = text.slice(0, iStart).split('\n').length - 1
-    const endLine = text.slice(0, iEnd).split('\n').length - 1
-    const newText = text
-        .split('\n')
-        .map((line, i) => {
-            if(i < startLine || i > endLine || nLevels === 0) {
-                newLine = line
-            }
-            else if(nLevels > 0) {
-                newLine = line.replace(/^/, '    ')
-            }
-            else if(nLevels < 0) {
-                newLine = line.replace(/^    /, '')
-            }
+const TextBox = {
+    autoSize: () => {
+        textbox.rows = textbox.value.split('\n').length
+    },
+    sendPost: () => {
+        if(textbox.value) {
+            wire({kind: 'post', value: textbox.value})
+            textbox.value = ''
+            textbox.focus()
+        }
+    },
+    blockIndent: (text, iStart, iEnd, nLevels) => {
+        const startLine = text.slice(0, iStart).split('\n').length - 1
+        const endLine = text.slice(0, iEnd).split('\n').length - 1
+        const newText = text
+            .split('\n')
+            .map((line, i) => {
+                if(i < startLine || i > endLine || nLevels === 0) {
+                    newLine = line
+                }
+                else if(nLevels > 0) {
+                    newLine = line.replace(/^/, '    ')
+                }
+                else if(nLevels < 0) {
+                    newLine = line.replace(/^    /, '')
+                }
 
-            if(i === startLine) {
-                iStart = iStart + newLine.length - line.length
-            }
-            iEnd = iEnd + newLine.length - line.length
-            return newLine
-        })
-        .join('\n')
-    return [newText, Math.max(0, iStart), Math.max(0, iEnd)]
-}
-const hotKey = (e) => {
-    // if isDesktop, Enter posts, unless Shift+Enter
-    // use isLandscape as proxy for isDesktop
-    if(e.key === 'Enter' && isLandscape && !e.shiftKey) {
-        e.preventDefault()
-        Chat.sendPost()
-    }
-    // indent and dedent
-    const modKey = e.ctrlKey || e.metaKey
-    const {value: text, selectionStart: A, selectionEnd: B} = textbox
-    if(e.key === 'Tab') {
-        e.preventDefault()
-        const regex = new RegExp(`([\\s\\S]{${A}})([\\s\\S]{${B - A}})`)
-        textbox.value = text.replace(regex, (m, a, b) => a + ' '.repeat(4))
-        textbox.setSelectionRange(A + 4, A + 4)
-    }
-    if(']['.includes(e.key) && modKey) {
-        e.preventDefault()
-        const nLevels = {']': 1, '[': -1}[e.key]
-        const [newText, newA, newB] = blockIndent(text, A, B, nLevels)
-        textbox.value = newText
-        textbox.setSelectionRange(newA, newB)
-    }
+                if(i === startLine) {
+                    iStart = iStart + newLine.length - line.length
+                }
+                iEnd = iEnd + newLine.length - line.length
+                return newLine
+            })
+            .join('\n')
+        return [newText, Math.max(0, iStart), Math.max(0, iEnd)]
+    },
+    hotKey: (e) => {
+        // if isDesktop, Enter posts, unless Shift+Enter
+        // use isLandscape as proxy for isDesktop
+        if(e.key === 'Enter' && isLandscape && !e.shiftKey) {
+            e.preventDefault()
+            TextBox.sendPost()
+        }
+        // indent and dedent
+        const modKey = e.ctrlKey || e.metaKey
+        const {value: text, selectionStart: A, selectionEnd: B} = textbox
+        if(e.key === 'Tab') {
+            e.preventDefault()
+            const regex = new RegExp(`([\\s\\S]{${A}})([\\s\\S]{${B - A}})`)
+            textbox.value = text.replace(regex, (m, a, b) => a + ' '.repeat(4))
+            textbox.setSelectionRange(A + 4, A + 4)
+        }
+        if(']['.includes(e.key) && modKey) {
+            e.preventDefault()
+            const nLevels = {']': 1, '[': -1}[e.key]
+            const [newText, newA, newB] = TextBox.blockIndent(text, A, B, nLevels)
+            textbox.value = newText
+            textbox.setSelectionRange(newA, newB)
+        }
+    },
+    view() {
+        return m('.actions',
+            m('textarea#textbox', {
+                oncreate: (vnode) => {
+                    TextBox.autoSize()
+                    autoFocus(vnode)
+                },
+                onkeydown: TextBox.hotKey,
+                onkeyup: TextBox.autoSize,
+            }),
+            m('button', {
+                onclick: ({target}) => {
+                    TextBox.sendPost()
+                    TextBox.autoSize()
+                },
+            },
+            'Send'),
+        )
+    },
 }
 const VideoOptions = {
     available: ['mirror', 'square', 'full-screen'],
         dom.autoplay = true
         dom.muted = (username === State.username)
         dom.srcObject = stream
-        dom.ondblclick = toggleFullscreen(dom)
     },
     view({attrs}) {
         const classList = VideoOptions.getClassListFor(attrs.username)
     },
 }
 const Chat = {
-    sendPost: () => {
-        if(textbox.value) {
-            wire({kind: 'post', value: textbox.value})
-            textbox.value = ''
-        }
+    prettifyTime: (ts) => {
+        const dt = new Date(ts)
+        const H = `0${dt.getHours()}`.slice(-2)
+        const M = `0${dt.getMinutes()}`.slice(-2)
+        const S = `0${dt.getSeconds()}`.slice(-2)
+        return `${H}:${M}:${S}`
     },
     view() {
         return m('.chat',
             m('.posts',
                 State.posts.map(post => m('.post', {oncreate: scrollIntoView},
-                    m('.ts', prettyTime(post.ts)),
+                    m('.ts', Chat.prettifyTime(post.ts)),
                     m('.source', post.source || '~'),
                     m('.text', m.trust(DOMPurify.sanitize(marked(post.value)))),
                 )),
             ),
-            m('.actions',
-                m('textarea#textbox', {oncreate: autoFocus, onkeydown: hotKey}),
-                m('button', {onclick: Chat.sendPost}, 'Send'),
-            ),
+            m(TextBox),
             m('.online',
                 m('button', {onclick: Login.sendLogout}, 'Logout'),
                 m('.user-list', State.online.map(username =>