Defensive Programming in JavaScript

1// Method 1: Input validation
2function processUserInput(input) {
3    if (typeof input !== 'string') {
4        throw new TypeError('Input must be a string');
5    }
6    
7    if (input.length === 0) {
8        throw new Error('Input cannot be empty');
9    }
10    
11    if (input.length > 100) {
12        throw new Error('Input too long');
13    }
14    
15    return input.trim();
16}
17
18// Method 2: Null/undefined checks
19function safeAccess(obj, path) {
20    const keys = path.split('.');
21    let current = obj;
22    
23    for (const key of keys) {
24        if (current == null) {
25            return null;
26        }
27        current = current[key];
28    }
29    
30    return current;
31}
32
33const user = { profile: { name: 'John' } };
34console.log('Name:', safeAccess(user, 'profile.name'));
35console.log('Missing:', safeAccess(user, 'profile.email'));
36
37// Method 3: Default values
38function getValue(value, defaultValue) {
39    return value != null ? value : defaultValue;
40}
41
42function processConfig(config) {
43    return {
44        timeout: getValue(config.timeout, 5000),
45        retries: getValue(config.retries, 3),
46        url: getValue(config.url, 'https://api.example.com')
47    };
48}
49
50// Method 4: Type checking
51function validateType(value, expectedType) {
52    const actualType = typeof value;
53    if (actualType !== expectedType) {
54        throw new TypeError(`Expected ${expectedType}, got ${actualType}`);
55    }
56    return value;
57}
58
59// Method 5: Range validation
60function validateRange(value, min, max) {
61    if (value < min || value > max) {
62        throw new RangeError(`Value must be between ${min} and ${max}`);
63    }
64    return value;
65}
66
67// Method 6: Safe array operations
68function safeArrayOperation(array, index, operation) {
69    if (!Array.isArray(array)) {
70        throw new TypeError('First argument must be an array');
71    }
72    
73    if (index < 0 || index >= array.length) {
74        return null;
75    }
76    
77    return operation(array[index]);
78}
79
80// Method 7: Error boundaries
81function withErrorBoundary(fn, fallback) {
82    try {
83        return fn();
84    } catch (error) {
85        console.error('Error in function:', error);
86        return fallback();
87    }
88}
89
90const result = withErrorBoundary(
91    () => riskyOperation(),
92    () => 'Default value'
93);