Static Members

Beginner~15 min

Static members belong to the class itself, not instances. They're perfect for utility functions and shared data.

Static Properties and Methods

Output

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Static vs Instance:

Static: Accessed via class name (e.g., Math.PI)
Instance: Accessed via object (e.g., user.name)
Static members are shared across all instances
Cannot access instance members from static methods

When to Use Static

Utility functions: Math operations, formatters
Constants: Shared configuration values
Factory methods: Alternative constructors
Counters: Track total instances

Common Mistakes

1. Accessing Instance Members from Static

class User {
    userName: string = "Alice";
    
    static greet() {
        console.log(this.userName);  // ✗ Error!
    }
}

// ✓ Static can only access static
class User {
    static defaultName = "Guest";
    
    static greet() {
        console.log(this.defaultName);  // ✓ OK
    }
}

2. Using 'this' Instead of Class Name

class Counter {
    static count = 0;
    
    increment() {
        this.count++;  // ✗ Wrong - 'this' is instance
    }
}

// ✓ Use class name
class Counter {
    static count = 0;
    
    increment() {
        Counter.count++;  // ✓ Correct
    }
}

Best Practice: Use static for utility functions that don't need instance data. Examples: Math.max(), Array.isArray()

Summary

Static members belong to the class, not instances
Access via class name: ClassName.member
Perfect for utilities, constants, factories
Cannot access instance members from static

What's Next?

Congratulations! Module 3 complete. Next: Advanced Types!

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Next Union Types →