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86The boolean Type
87The number Type
88The string Type
89The bigint Type
90The symbol Type
91null and undefined as Types
92Type Annotations for Primitives
93Literal Values vs Type Names
94Type Inference with Primitives
95The void Type for No Return
96Primitive Wrappers: Number, String, Boolean
97Assignability Between Primitives
98Primitive Type Widening on Reassignment
99Using const for Literal Narrowing
100strictNullChecks and Primitive Assignability
101Primitive Union Types
102Type Guards for Primitives
103Common Primitive Pitfalls
104Array Type Syntax: T[] vs Array<T>
105Typed Array Literals
106Empty Array Initialization
107Array Methods Return Typed Results
108Readonly Arrays
109Arrays of Union Types
110Multidimensional Arrays
111Array Type Guards and Narrowing
112Rest Parameters as Arrays
113Array Destructuring with Types
114Fixed-Length Arrays vs Tuples
115Common Array Type Pitfalls
116What Tuples Are and When to Use Them
117Declaring Tuple Types
118Accessing Tuple Elements
119Tuple Length and Array Methods
120Optional Tuple Elements
121Rest Elements in Tuples
122Readonly Tuples
123Labeled Tuple Elements
124Tuples vs Arrays
125Common Tuple Use Cases
126Introduction to any: The Opt-Out Type
127When any Appears by Default
128The Danger of any: Type Safety Lost
129Introduction to unknown: The Type-Safe any
130Assigning to unknown
131Using unknown Values Safely
132Narrowing unknown with typeof
133Narrowing unknown with instanceof and in
134Introduction to never: The Bottom Type
135Functions That Return never
136never in Exhaustive Union Checks
137never as an Impossible Intersection
138Assigning to never
139Comparing any, unknown, and never
140Choosing Between any and unknown

86The boolean Type
87The number Type
88The string Type
89The bigint Type
90The symbol Type
91null and undefined as Types
92Type Annotations for Primitives
93Literal Values vs Type Names
94Type Inference with Primitives
95The void Type for No Return
96Primitive Wrappers: Number, String, Boolean
97Assignability Between Primitives
98Primitive Type Widening on Reassignment
99Using const for Literal Narrowing
100strictNullChecks and Primitive Assignability
101Primitive Union Types
102Type Guards for Primitives
103Common Primitive Pitfalls
104Array Type Syntax: T[] vs Array<T>
105Typed Array Literals
106Empty Array Initialization
107Array Methods Return Typed Results
108Readonly Arrays
109Arrays of Union Types
110Multidimensional Arrays
111Array Type Guards and Narrowing
112Rest Parameters as Arrays
113Array Destructuring with Types
114Fixed-Length Arrays vs Tuples
115Common Array Type Pitfalls
116What Tuples Are and When to Use Them
117Declaring Tuple Types
118Accessing Tuple Elements
119Tuple Length and Array Methods
120Optional Tuple Elements
121Rest Elements in Tuples
122Readonly Tuples
123Labeled Tuple Elements
124Tuples vs Arrays
125Common Tuple Use Cases
126Introduction to any: The Opt-Out Type
127When any Appears by Default
128The Danger of any: Type Safety Lost
129Introduction to unknown: The Type-Safe any
130Assigning to unknown
131Using unknown Values Safely
132Narrowing unknown with typeof
133Narrowing unknown with instanceof and in
134Introduction to never: The Bottom Type
135Functions That Return never
136never in Exhaustive Union Checks
137never as an Impossible Intersection
138Assigning to never
139Comparing any, unknown, and never
140Choosing Between any and unknown

Lesson 133 of 1,796·3. Basic TypesPro lesson

Narrowing unknown with instanceof and in

Apply structural checks to narrow unknown to object or class types.

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