refactor: ES6+ modernization + 2 bugfixes

- var→const/let, function→arrow/class across all 13 JS files
- Timer: prototype→class with ES6 getters
- plan days: IIFE→Array.from declarative generation
- storage/plan: unified formatDate via util.js
- Bugfix: getPlanDay now filters by planId (plan switch accuracy)
- Bugfix: getTodayRecord searches all months (cross-month boundary)
- WXML/WXSS unchanged; public API unchanged

utils/util.js

@@ -1,31 +1,28 @@
-function formatTime(seconds) {
-  var m = Math.floor(seconds / 60)
-  var s = seconds % 60
-  return (m < 10 ? '0' : '') + m + ':' + (s < 10 ? '0' : '') + s
+const formatTime = (seconds) => {
+  const m = Math.floor(seconds / 60)
+  const s = seconds % 60
+  return `${String(m).padStart(2, '0')}:${String(s).padStart(2, '0')}`
 }
 
-function formatDuration(seconds) {
-  if (seconds < 60) return seconds + '秒'
-  var m = Math.floor(seconds / 60)
-  var s = seconds % 60
-  return s > 0 ? m + '分' + s + '秒' : m + '分钟'
+const formatDuration = (seconds) => {
+  if (seconds < 60) return `${seconds}秒`
+  const m = Math.floor(seconds / 60)
+  const s = seconds % 60
+  return s > 0 ? `${m}分${s}秒` : `${m}分钟`
 }
 
-function getDaysInMonth(year, month) {
-  return new Date(year, month, 0).getDate()
-}
+const getDaysInMonth = (year, month) => new Date(year, month, 0).getDate()
 
-function getMonthCalendar(year, month) {
-  var firstDay = new Date(year, month - 1, 1)
-  var lastDay = new Date(year, month, 0)
-  var daysInMonth = lastDay.getDate()
-  var startDayOfWeek = firstDay.getDay()
+const getMonthCalendar = (year, month) => {
+  const firstDay = new Date(year, month - 1, 1)
+  const daysInMonth = new Date(year, month, 0).getDate()
+  const startDayOfWeek = firstDay.getDay()
 
-  var weeks = []
-  var week = [null, null, null, null, null, null, null]
+  const weeks = []
+  let week = [null, null, null, null, null, null, null]
 
-  for (var d = 1; d <= daysInMonth; d++) {
-    var dow = (startDayOfWeek + d - 1) % 7
+  for (let d = 1; d <= daysInMonth; d++) {
+    const dow = (startDayOfWeek + d - 1) % 7
     week[dow] = d
     if (dow === 6 || d === daysInMonth) {
       weeks.push(week.slice())
@@ -36,9 +33,17 @@ function getMonthCalendar(year, month) {
   return weeks
 }
 
-module.exports = {
-  formatTime: formatTime,
-  formatDuration: formatDuration,
-  getDaysInMonth: getDaysInMonth,
-  getMonthCalendar: getMonthCalendar
+const formatDate = (date) => {
+  const y = date.getFullYear()
+  const m = String(date.getMonth() + 1).padStart(2, '0')
+  const d = String(date.getDate()).padStart(2, '0')
+  return `${y}-${m}-${d}`
+}
+
+module.exports = {
+  formatTime,
+  formatDuration,
+  getDaysInMonth,
+  getMonthCalendar,
+  formatDate
 }