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236Function Type Syntax
237Arrow Function Type Annotations
238Return Type Inference
239void Return Type
240Function Type Expressions
241Call Signatures
242Construct Signatures
243Parameter Type Inference from Context
244Explicitly Typing Callback Parameters
245Typing Anonymous Functions
246noImplicitAny and Functions
247Functions as Values
248Method Shorthand Typing
249Return Type Annotations Best Practices
250Optional Parameters with ?
251Optional Parameters Must Come Last
252Default Parameter Values
253Default Parameters Are Implicitly Optional
254Type Annotations with Defaults
255undefined vs Omission
256Optional vs undefined Union Types
257Destructured Parameters with Defaults
258Default Parameters in Arrow Functions
259Common Patterns: Config Objects
260Rest Parameters Basics
261Typing Rest Parameters Explicitly
262Rest Parameters with Tuple Types
263Spread Operator in Function Calls
264Combining Fixed and Rest Parameters
265Rest Parameters in Callback Functions
266Spreading Tuples with Known Length
267Rest Parameters vs Array Parameters
268What Are Function Overloads?
269Overload Syntax: Signatures vs Implementation
270Why Overloads Are Needed
271Simple Overload Example
272The Implementation Signature Must Be Compatible
273Overload Resolution Order Matters
274Overloading by Arity
275Overloading by Parameter Type
276Common Pitfalls with Overloads
277Overloads vs Conditional Types
278Overloads vs Union Parameters
279Real-World Overload Examples
280The Problem: Losing this in JavaScript
281Declaring this as the First Parameter
282this Parameter in Methods
283this: void for No-Context Functions
284ThisParameterType and OmitThisParameter Utilities
285Arrow Functions and this Capture
286this in Callback Typing
287When this Parameter Typing Matters

236Function Type Syntax
237Arrow Function Type Annotations
238Return Type Inference
239void Return Type
240Function Type Expressions
241Call Signatures
242Construct Signatures
243Parameter Type Inference from Context
244Explicitly Typing Callback Parameters
245Typing Anonymous Functions
246noImplicitAny and Functions
247Functions as Values
248Method Shorthand Typing
249Return Type Annotations Best Practices
250Optional Parameters with ?
251Optional Parameters Must Come Last
252Default Parameter Values
253Default Parameters Are Implicitly Optional
254Type Annotations with Defaults
255undefined vs Omission
256Optional vs undefined Union Types
257Destructured Parameters with Defaults
258Default Parameters in Arrow Functions
259Common Patterns: Config Objects
260Rest Parameters Basics
261Typing Rest Parameters Explicitly
262Rest Parameters with Tuple Types
263Spread Operator in Function Calls
264Combining Fixed and Rest Parameters
265Rest Parameters in Callback Functions
266Spreading Tuples with Known Length
267Rest Parameters vs Array Parameters
268What Are Function Overloads?
269Overload Syntax: Signatures vs Implementation
270Why Overloads Are Needed
271Simple Overload Example
272The Implementation Signature Must Be Compatible
273Overload Resolution Order Matters
274Overloading by Arity
275Overloading by Parameter Type
276Common Pitfalls with Overloads
277Overloads vs Conditional Types
278Overloads vs Union Parameters
279Real-World Overload Examples
280The Problem: Losing this in JavaScript
281Declaring this as the First Parameter
282this Parameter in Methods
283this: void for No-Context Functions
284ThisParameterType and OmitThisParameter Utilities
285Arrow Functions and this Capture
286this in Callback Typing
287When this Parameter Typing Matters

Lesson 256 of 1,796·6. FunctionsPro lesson

Optional vs undefined Union Types

The subtle difference between param?: T and param: T | undefined and when each matters.

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