TypeScript Interview Questions

🟢 Basic Level (1–20)

1. What is TypeScript?
2. Who developed TypeScript?
3. Is TypeScript a programming language?
4. Difference between TypeScript and JavaScript?
5. Why do we use TypeScript?
6. What are the features of TypeScript?
7. How does TypeScript compile?
8. What is static typing?
9. What is type inference?
10. What is the file extension of TypeScript?
11. What is tsconfig.json?
12. What is type annotation?
13. What is any type?
14. What is unknown type?
15. Difference between any and unknown?
16. What are primitive types in TypeScript?
17. What is boolean, number, string types?
18. What is void type?
19. What is never type?
20. What is null and undefined?

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⚙️ Core Concepts (21–40)

21. What are interfaces in TypeScript?
22. Difference between interface and type alias?
23. What is optional property?
24. What are arrays in TypeScript?
25. What are tuples?
26. What are enums?
27. What is union type?
28. What is intersection type?
29. What are literals in TypeScript?
30. What is type narrowing?
31. What is type assertion?
32. What is type casting?
33. What are generics?
34. Why use generics?
35. What is function typing?
36. What are arrow functions in TypeScript?
37. What is overload function?
38. What is default parameter?
39. What is rest parameter?
40. What is object typing?

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🧱 OOP & Advanced Concepts (41–60)

41. What is OOP in TypeScript?
42. What is class in TypeScript?
43. What are constructors?
44. What is inheritance?
45. What is polymorphism?
46. What is encapsulation?
47. What are access modifiers?
48. Difference between public, private, protected?
49. What is abstract class?
50. What are interfaces used for in OOP?
51. What are getters and setters?
52. What is static keyword?
53. What is method overriding?
54. What is method overloading?
55. What is namespace?
56. What is module in TypeScript?
57. What is import/export?
58. What is decorators?
59. What are metadata in TypeScript?
60. What is compilation target?

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⚡ Advanced Level (61–80)

61. What is structural typing?
62. What is duck typing?
63. What is type compatibility?
64. What is mapped type?
65. What is conditional type?
66. What is keyof operator?
67. What is typeof operator in TS?
68. What is indexed access type?
69. What is utility types in TypeScript?
70. Name common utility types (Partial, Pick, Omit, etc.)
71. What is Partial<T>?
72. What is Required<T>?
73. What is Readonly<T>?
74. What is Record<K, T>?
75. What is Exclude<T, U>?
76. What is Extract<T, U>?
77. What is NonNullable<T>?
78. What is ReturnType<T>?
79. What is Parameters<T>?
80. What is type guards?

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🚀 Scenario-Based (81–100)

81. How does TypeScript improve JavaScript?
82. How does TypeScript prevent runtime errors?
83. How to migrate JS project to TS?
84. How does TypeScript compile to JavaScript?
85. How to configure tsconfig.json?
86. How to enable strict mode?
87. How to handle API response typing?
88. How to type React props in TypeScript?
89. How to use TypeScript with Node.js?
90. How to debug TypeScript code?
91. How to handle errors in TypeScript?
92. How to use TypeScript in large projects?
93. How does TypeScript improve code maintainability?
94. Difference between compile-time and runtime?
95. How to use interfaces in real projects?
96. What are best practices in TypeScript?
97. What are common TypeScript mistakes?
98. How to optimize TypeScript performance?
99. Why use TypeScript with React or Angular?
100. Why companies prefer TypeScript?

TypeScript Interview Answers (Q1–100)

🟢 Basic (1–20)

1. TypeScript is a typed superset of JavaScript
2. Microsoft developed TypeScript
3. No, it is a superset of JavaScript
4. TS has types, JS is dynamically typed
5. To reduce runtime errors and improve code quality
6. Static typing, interfaces, OOP support
7. It compiles to JavaScript using tsc
8. Types defined before runtime
9. Type is automatically detected
10. .ts
11. Configuration file for TypeScript compiler
12. Defining type for variables
13. Any type disables type checking
14. Unknown requires type checking before use
15. Any = no safety, Unknown = safe
16. number, string, boolean, etc.
17. Basic primitive data types
18. Function returns nothing
19. Function never returns value
20. null = empty, undefined = not assigned

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⚙️ Core (21–40)

21. Blueprint of object
22. Interface = object structure, type = flexible alias
23. Optional property uses “?”
24. Same type elements collection
25. Fixed-length mixed-type array
26. Named constant values
27. Multiple possible types
28. Combine multiple types
29. Fixed values
30. Refining types
31. Forcing type conversion
32. Similar to assertion but unsafe
33. Reusable type parameters
34. Code reusability
35. Function with types
36. Function shorthand syntax
37. Same function multiple signatures
38. Default value parameter
39. Variable number of arguments
40. Object structure typing

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🧱 OOP (41–60)

41. Object-oriented programming
42. Blueprint for objects
43. Initializes object
44. Inherits properties
45. One function, multiple forms
46. Data hiding
47. Access control keywords
48. Public = open, private = restricted, protected = subclass only
49. Class with abstract methods
50. Define structure
51. Get/set values
52. Class-level member
53. Redefining method
54. Same function different parameters
55. Grouping code (deprecated mostly)
56. ES module system
57. Sharing code
58. Special function metadata
59. Extra class information
60. ES target version

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⚡ Advanced (61–80)

61. Shape-based typing
62. Same as structural typing
63. Type compatibility rules
64. Create new types from existing
65. Type based on condition
66. Gets keys of type
67. Gets type of variable
68. Access nested types
69. Predefined helper types
70. Partial, Pick, Omit, Record etc.
71. Makes all properties optional
72. Makes all required
73. Makes all readonly
74. Creates object type
75. Excludes types
76. Extracts matching types
77. Removes null/undefined
78. Return type of function
79. Function parameter types
80. Type checking conditions

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🚀 Scenario (81–100)

81. Adds type safety
82. Catches errors at compile time
83. Rename files + add tsconfig
84. TS → JS compiler output
85. Config compiler options
86. Enables strict checking
87. Define interface for API data
88. Use interface for props typing
89. Use ts-node or compilation
90. Use debugger + compiler errors
91. Try/catch + strict typing
92. Better structure + safety
93. Reduces bugs
94. Compile vs execution time
95. Define reusable structures
96. Use strict mode, interfaces
97. Overusing any type
98. Avoid unnecessary types
99. Better scalability and safety
100. Safer and scalable development

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