TypeScript Null and Undefined

In JavaScript, many bugs happen because values are missing.

  TypeScript helps you **handle missing values safely**.
  
  ## What are null and undefined?
  
  - undefined: value not assigned
  - null: intentionally empty
  
  ```ts
  let a: number;
  console.log(a); // undefined
  
  let b: number | null = null;
  ```
  
  ## The problem in JavaScript
  
  ```ts
  let name = null;
  console.log(name.length); // crash at runtime
  ```
  
  ## TypeScript safety
  
  ```ts
  let name: string | null = null;
  // name.length ❌ error
  if (name) {
    console.log(name.length); // safe
  }
  ```
  
  ## strictNullChecks
  
  When enabled:
  - null/undefined must be handled explicitly
  - prevents runtime crashes
  
  ## Optional chaining
  
  ```ts
  type User = { profile?: { email: string } };
  
  const user: User = {};
  console.log(user.profile?.email); // undefined, safe
  ```
  
  ## Graph
  
  ```mermaid
  flowchart LR
    A[Value] --> B{null/undefined?}
    B -->|Yes| C[Handle safely]
    B -->|No| D[Use value]
  ```
  
  ## Remember
  - Always handle null/undefined
  - Use strictNullChecks
  - Optional chaining avoids crashes