1const validators = {
2    required: (value) => !value ? "This field is required" : null,
3    minLength: (value, min) => value.length < min ? `Minimum length is ${min}` : null,
4    email: (value) => !value.includes('@') ? "Invalid email format" : null,
5    password: (value) => !/[A-Z]/.test(value) ? "Must contain uppercase letter" : null
6};
7
8function validateField(value, rules) {
9    const errors = Object.entries(rules)
10        .map(([rule, param]) => {
11            if (validators[rule]) {
12                return validators[rule](value, param);
13            }
14            return null;
15        })
16        .filter(Boolean);
17    
18    return errors[0] || null;
19}
20
21// Usage example:
22const rules = {
23    required: true,
24    minLength: 8,
25    password: true
26};
27
28const result = validateField("password123", rules);