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382What Union Types Are
383Creating Simple Union Types
384Union Type Syntax and Readability
385Type Checking with Unions
386Common Properties Access
387Unions vs Overloads
388Union Types in Function Parameters
389Union Types in Return Values
390Arrays of Union Types
391Union Order and Duplicate Types
392What Narrowing Means for Unions
393typeof Guards for Primitive Unions
394Equality Checks as Narrowing
395Truthiness Narrowing with Unions
396The in Operator for Object Unions
397instanceof for Class Unions
398Type Predicates for Custom Narrowing
399Narrowing with Discriminant Properties
400switch Statements and Union Narrowing
401Array.isArray for Array vs Non-Array
402Combining Multiple Narrowing Techniques
403Control Flow Analysis Limitations
404What Is a Discriminated Union?
405The Discriminant Property
406Basic Discriminated Union Example
407Narrowing with switch Statements
408Narrowing with if/else Chains
409Multiple Discriminants in One Union
410Discriminated Unions for State Machines
411Result Types with Discriminated Unions
412Exhaustiveness Checking with never
413Common Discriminant Names
414Discriminated Unions vs Enums
415Nested Discriminated Unions
416Adding Variants Without Breaking Code
417Discriminated Unions in Redux Actions
418When Discriminated Unions Shine
419What Exhaustive Matching Means
420The never Type in Switch Statements
421Exhaustiveness Checking with Discriminated Unions
422The assertNever Helper Function
423Compile-Time vs Runtime Guarantees
424Adding New Union Variants Safely
425Exhaustiveness in Functional Patterns
426When Exhaustiveness Isn't Needed
427Exhaustive Matching with Return Types
428Common Pitfalls and Edge Cases

382What Union Types Are
383Creating Simple Union Types
384Union Type Syntax and Readability
385Type Checking with Unions
386Common Properties Access
387Unions vs Overloads
388Union Types in Function Parameters
389Union Types in Return Values
390Arrays of Union Types
391Union Order and Duplicate Types
392What Narrowing Means for Unions
393typeof Guards for Primitive Unions
394Equality Checks as Narrowing
395Truthiness Narrowing with Unions
396The in Operator for Object Unions
397instanceof for Class Unions
398Type Predicates for Custom Narrowing
399Narrowing with Discriminant Properties
400switch Statements and Union Narrowing
401Array.isArray for Array vs Non-Array
402Combining Multiple Narrowing Techniques
403Control Flow Analysis Limitations
404What Is a Discriminated Union?
405The Discriminant Property
406Basic Discriminated Union Example
407Narrowing with switch Statements
408Narrowing with if/else Chains
409Multiple Discriminants in One Union
410Discriminated Unions for State Machines
411Result Types with Discriminated Unions
412Exhaustiveness Checking with never
413Common Discriminant Names
414Discriminated Unions vs Enums
415Nested Discriminated Unions
416Adding Variants Without Breaking Code
417Discriminated Unions in Redux Actions
418When Discriminated Unions Shine
419What Exhaustive Matching Means
420The never Type in Switch Statements
421Exhaustiveness Checking with Discriminated Unions
422The assertNever Helper Function
423Compile-Time vs Runtime Guarantees
424Adding New Union Variants Safely
425Exhaustiveness in Functional Patterns
426When Exhaustiveness Isn't Needed
427Exhaustive Matching with Return Types
428Common Pitfalls and Edge Cases

Lesson 398 of 1,796·9. Union TypesPro lesson

Type Predicates for Custom Narrowing

Writing user-defined type guards that return 'value is Type' for complex unions.

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