Storage Migration in JavaScript

1// Method 1: Simple migration
2function migrateStorage() {
3    const oldData = localStorage.getItem('oldKey');
4    if (oldData) {
5        // Migrate to new format
6        const newData = {
7            version: 2,
8            data: JSON.parse(oldData)
9        };
10        localStorage.setItem('newKey', JSON.stringify(newData));
11        localStorage.removeItem('oldKey');
12        console.log('Migration complete');
13    }
14}
15
16// Method 2: Version-based migration
17const STORAGE_VERSION = 2;
18
19function checkAndMigrate() {
20    const currentVersion = localStorage.getItem('storageVersion');
21    
22    if (!currentVersion || parseInt(currentVersion) < STORAGE_VERSION) {
23        console.log('Migration needed');
24        migrateToVersion(parseInt(currentVersion) || 1);
25        localStorage.setItem('storageVersion', STORAGE_VERSION.toString());
26    }
27}
28
29function migrateToVersion(fromVersion) {
30    if (fromVersion === 1) {
31        // Migrate from v1 to v2
32        const v1Data = localStorage.getItem('userData');
33        if (v1Data) {
34            const data = JSON.parse(v1Data);
35            const v2Data = {
36                ...data,
37                metadata: {
38                    createdAt: new Date().toISOString(),
39                    version: 2
40                }
41            };
42            localStorage.setItem('userData', JSON.stringify(v2Data));
43        }
44    }
45}
46
47checkAndMigrate();
48
49// Method 3: Migration with backup
50function migrateWithBackup() {
51    // Create backup
52    const backup = {};
53    for (let i = 0; i < localStorage.length; i++) {
54        const key = localStorage.key(i);
55        backup[key] = localStorage.getItem(key);
56    }
57    localStorage.setItem('backup_' + Date.now(), JSON.stringify(backup));
58    
59    // Perform migration
60    try {
61        migrateStorage();
62        console.log('Migration successful');
63    } catch (e) {
64        console.error('Migration failed, restoring backup');
65        // Restore from backup
66        restoreBackup(backup);
67    }
68}
69
70function restoreBackup(backup) {
71    localStorage.clear();
72    Object.keys(backup).forEach(key => {
73        localStorage.setItem(key, backup[key]);
74    });
75}
76
77// Method 4: Progressive migration
78function progressiveMigration() {
79    const migrationSteps = [
80        () => migrateStep1(),
81        () => migrateStep2(),
82        () => migrateStep3()
83    ];
84    
85    migrationSteps.forEach((step, index) => {
86        try {
87            step();
88            console.log(`Step ${index + 1} complete`);
89        } catch (e) {
90            console.error(`Step ${index + 1} failed:`, e);
91            throw e;
92        }
93    });
94}
95
96function migrateStep1() {
97    // Step 1 logic
98}
99
100function migrateStep2() {
101    // Step 2 logic
102}
103
104function migrateStep3() {
105    // Step 3 logic
106}
107
108// Method 5: Data transformation
109function transformData(oldFormat) {
110    // Transform old format to new format
111    return {
112        id: oldFormat.userId,
113        name: oldFormat.fullName,
114        email: oldFormat.emailAddress,
115        settings: {
116            theme: oldFormat.theme || 'light',
117            notifications: oldFormat.notify || true
118        }
119    };
120}
121
122function migrateUserData() {
123    const oldData = localStorage.getItem('oldUserData');
124    if (oldData) {
125        const parsed = JSON.parse(oldData);
126        const newData = transformData(parsed);
127        localStorage.setItem('userData', JSON.stringify(newData));
128        localStorage.removeItem('oldUserData');
129    }
130}