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141What Is Type Inference?
142Basic Variable Inference
143Array and Object Literal Inference
144Function Return Type Inference
145Best Common Type Algorithm
146Widening: From Literal to Broader Types
147Const vs Let: Inference Differences
148Parameter Inference in Callbacks
149Inference Through Control Flow
150Generic Type Argument Inference
151Tuple Inference vs Array Inference
152Inference Limitations with Empty Values
153Reverse Inference: From Usage to Definition
154The Role of noImplicitAny
155The Default Rule: Let TypeScript Infer
156Annotating Function Parameters
157Inferring vs Annotating Return Types
158Variable Declaration: When to Annotate
159Annotating for Documentation Value
160Inference Across Module Boundaries
161Complex Inference and Readability Trade-offs
162Annotating to Enforce Constraints
163Literals and Widening: When Inference Hurts
164Type Inference in Arrays and Objects
165Inference with Third-Party Libraries
166Balancing Inference and Explicitness in Teams
167What Is Contextual Typing
168Function Parameter Context
169Array Method Callbacks
170Event Handler Context
171Return Type Context
172Object Literal Context
173Contextual Union Types
174Best Common Type in Context
175When Context Isn't Enough
176Contextual Typing Trade-offs
177Array Literals Inferred as Mutable Arrays
178Object Literals Widening to General Types
179Implicit any from Untyped Parameters
180Lost Precision with Intermediate Variables
181Empty Array Inference Problems
182Callback Parameter Inference Gaps
183Return Type Inference with Multiple Returns
184Destructuring Inference Limitations
185Inference with Third-Party Libraries
186Evolution of Implicit any Types
187Generic Inference Falling Back to Unknown
188Contextual Typing Not Applied Everywhere

141What Is Type Inference?
142Basic Variable Inference
143Array and Object Literal Inference
144Function Return Type Inference
145Best Common Type Algorithm
146Widening: From Literal to Broader Types
147Const vs Let: Inference Differences
148Parameter Inference in Callbacks
149Inference Through Control Flow
150Generic Type Argument Inference
151Tuple Inference vs Array Inference
152Inference Limitations with Empty Values
153Reverse Inference: From Usage to Definition
154The Role of noImplicitAny
155The Default Rule: Let TypeScript Infer
156Annotating Function Parameters
157Inferring vs Annotating Return Types
158Variable Declaration: When to Annotate
159Annotating for Documentation Value
160Inference Across Module Boundaries
161Complex Inference and Readability Trade-offs
162Annotating to Enforce Constraints
163Literals and Widening: When Inference Hurts
164Type Inference in Arrays and Objects
165Inference with Third-Party Libraries
166Balancing Inference and Explicitness in Teams
167What Is Contextual Typing
168Function Parameter Context
169Array Method Callbacks
170Event Handler Context
171Return Type Context
172Object Literal Context
173Contextual Union Types
174Best Common Type in Context
175When Context Isn't Enough
176Contextual Typing Trade-offs
177Array Literals Inferred as Mutable Arrays
178Object Literals Widening to General Types
179Implicit any from Untyped Parameters
180Lost Precision with Intermediate Variables
181Empty Array Inference Problems
182Callback Parameter Inference Gaps
183Return Type Inference with Multiple Returns
184Destructuring Inference Limitations
185Inference with Third-Party Libraries
186Evolution of Implicit any Types
187Generic Inference Falling Back to Unknown
188Contextual Typing Not Applied Everywhere

Lesson 158 of 1,796·4. Type InferencePro lesson

Variable Declaration: When to Annotate

How to decide whether const, let, and var declarations benefit from explicit types versus relying on inference.

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