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/plan.js

@@ -1,73 +1,52 @@
-var plans = {
+const { formatDate } = require('./util')
+
+const plans = {
   beginner: {
     id: 'beginner',
     name: '初级 (7天)',
     totalDays: 7,
     description: '适合初学者，从30秒起步',
-    days: [
-      { day: 1, target: 30 },
-      { day: 2, target: 40 },
-      { day: 3, target: 50 },
-      { day: 4, target: 60 },
-      { day: 5, target: 70 },
-      { day: 6, target: 80 },
-      { day: 7, target: 90 }
-    ]
+    days: Array.from({ length: 7 }, (_, i) => ({ day: i + 1, target: 30 + i * 10 }))
   },
   intermediate: {
     id: 'intermediate',
     name: '中级 (14天)',
     totalDays: 14,
     description: '有一定基础，从60秒起步',
-    days: [
-      { day: 1, target: 60 }, { day: 2, target: 60 },
-      { day: 3, target: 75 }, { day: 4, target: 75 },
-      { day: 5, target: 90 }, { day: 6, target: 90 },
-      { day: 7, target: 105 }, { day: 8, target: 105 },
-      { day: 9, target: 120 }, { day: 10, target: 120 },
-      { day: 11, target: 135 }, { day: 12, target: 135 },
-      { day: 13, target: 150 }, { day: 14, target: 150 }
-    ]
+    days: Array.from({ length: 14 }, (_, i) => {
+      const pair = Math.floor(i / 2)
+      return { day: i + 1, target: 60 + pair * 15 }
+    })
   },
   advanced: {
     id: 'advanced',
     name: '高级 (30天)',
     totalDays: 30,
     description: '挑战自我，从90秒起步',
-    days: (function () {
-      var arr = []
-      for (var i = 1; i <= 30; i++) {
-        arr.push({ day: i, target: 90 + Math.floor((i - 1) / 3) * 15 })
-      }
-      return arr
-    })()
+    days: Array.from({ length: 30 }, (_, i) => ({
+      day: i + 1,
+      target: 90 + Math.floor(i / 3) * 15
+    }))
   }
 }
 
-function getPlan(planId) {
-  return plans[planId] || plans.beginner
+const getPlan = (planId) => plans[planId] || plans.beginner
+
+const getTodayTarget = (planId, currentDay) => {
+  const plan = getPlan(planId)
+  const day = plan.days.find(d => d.day === currentDay)
+  return day ? day.target : plan.days[0].target
 }
 
-function getTodayTarget(planId, currentDay) {
-  var plan = getPlan(planId)
-  for (var i = 0; i < plan.days.length; i++) {
-    if (plan.days[i].day === currentDay) return plan.days[i].target
-  }
-  return plan.days[0].target
-}
-
-function getPlanDay(planId, records) {
-  var plan = getPlan(planId)
-  var now = new Date()
-  var today = now.getFullYear() + '-' +
-    ('0' + (now.getMonth() + 1)).slice(-2) + '-' +
-    ('0' + now.getDate()).slice(-2)
-  var dates = {}
-  records.forEach(function (r) {
-    if (r.date !== today) dates[r.date] = true
-  })
-  var trainedDays = Object.keys(dates).length
+const getPlanDay = (planId, records) => {
+  const plan = getPlan(planId)
+  const today = formatDate(new Date())
+  const trainedDays = new Set(
+    records
+      .filter(r => r.date !== today && r.planId === planId)
+      .map(r => r.date)
+  ).size
   return Math.min(trainedDays + 1, plan.totalDays)
 }
 
-module.exports = { plans: plans, getPlan: getPlan, getTodayTarget: getTodayTarget, getPlanDay: getPlanDay }
+module.exports = { plans, getPlan, getTodayTarget, getPlanDay }