Answer:<\/strong><\/p>\n\n\n\nType assertions are a way to override TypeScript\u2019s inferred type system. They allow developers to manually specify a type when the compiler cannot determine it accurately.<\/p>\n\n\n\n
Syntax:<\/strong><\/p>\n\n\n\nUsing as:<\/strong><\/p>\n\n\n\nlet value: unknown = \"TypeScript\";\nlet length: number = (value as string).length; \/\/ Treats value as a string<\/code><\/pre>\n\n\n\nUsing angle brackets (not in React):<\/strong><\/p>\n\n\n\nlet length: number = (<string>value).length;<\/code><\/pre>\n\n\n\nKey Points:<\/strong><\/p>\n\n\n\n\n- Not runtime casting<\/strong>: Type assertions do not change the actual runtime type; they only affect compile-time type checking.<\/li>\n\n\n\n
- Use cautiously when you\u2019re certain of the type to avoid runtime errors.<\/li>\n<\/ul>\n\n\n\n
Use Case:<\/strong> Commonly used with any or unknown types, such as when working with untyped libraries, dynamic data, or DOM manipulation:<\/p>\n\n\n\nconst input = document.getElementById(\"username\") as HTMLInputElement;\nconsole.log(input.value); \/\/ Assumes 'input' is of type HTMLInputElement<\/code><\/pre>\n\n\n\nIntermediate TypeScript Interview Questions and Answers<\/strong><\/strong><\/h3>\n\n\n\n11) How does TypeScript support inheritance?<\/strong><\/p>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\nTypeScript supports inheritance through the extends keyword, which allows one class (subclass) to inherit properties and methods from another class (superclass). This enables code reuse, polymorphism, and extending base functionality.
TypeScript also supports class-based inheritance<\/strong>, where methods and properties are shared across instances of the subclass, reducing redundancy.<\/p>\n\n\n\nExample<\/strong>:<\/p>\n\n\n\nclass Animal {\n name: string;\n constructor(name: string) {\n this.name = name;\n }\n move() {\n console.log(`${this.name} is moving`);\n }\n}\n\nclass Dog extends Animal {\n constructor(name: string) {\n super(name); \/\/ Calls the parent class constructor\n }\n bark() {\n console.log(`${this.name} barks!`);\n }\n}\n\nconst myDog = new Dog(\"Rex\");\nmyDog.move(); \/\/ Rex is moving\nmyDog.bark(); \/\/ Rex barks!<\/code><\/pre>\n\n\n\nKey Concepts<\/strong>:<\/p>\n\n\n\n\n- Inheritance<\/strong> allows subclass instances to access methods and properties of the superclass.<\/li>\n\n\n\n
- Polymorphism<\/strong>: Subclasses can override methods from parent classes.<\/li>\n<\/ul>\n\n\n\n
12) What are generics?<\/strong><\/p>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\nGenerics<\/strong> are a powerful feature in TypeScript that allows developers to write flexible, reusable code that works with any data type. Rather than defining a function or class for specific data types, generics allow you to write components that work with any type while maintaining type safety.<\/p>\n\n\n\nGenerics are defined using angle brackets (<T>) and provide type parameters that are replaced with actual types during function calls or class instantiations.<\/p>\n\n\n\n
Example<\/strong>:<\/p>\n\n\n\nfunction identity<T>(arg: T): T {\n return arg; \/\/ T will be replaced by the actual type at call time\n}\nconsole.log(identity<number>(42)); \/\/ Returns 42\nconsole.log(identity<string>(\"Hello\")); \/\/ Returns \"Hello\"<\/code><\/pre>\n\n\n\nUse Case<\/strong>: Useful for collections, APIs, or utilities that need to support multiple data types while ensuring type consistency.<\/p>\n\n\n\n13) What is the difference between type aliases and interfaces?<\/strong><\/p>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\nType Aliases<\/strong>: Type aliases define custom types for primitives, objects, and unions. They cannot be merged or extended once defined. They’re ideal for union types, intersections, or complex object types.<\/p>\n\n\n\nExample<\/strong>:<\/p>\n\n\n\ntype Point = { x: number; y: number };\ntype ID = number | string;<\/code><\/pre>\n\n\n\nInterfaces<\/strong>: Interfaces define the structure of an object and can be extended or merged with other interfaces. They are more flexible and better suited for defining contracts for objects, classes, and functions.<\/p>\n\n\n\nExample<\/strong>:<\/p>\n\n\n\ninterface Point { x: number; y: number; }<\/code><\/pre>\n\n\n\nKey Difference<\/strong>:<\/p>\n\n\n\n\n- Extensibility<\/strong>: Interfaces can be extended or merged; type aliases cannot.<\/li>\n\n\n\n
- Use Case<\/strong>: Use interfaces<\/strong> when defining object structures and type aliases<\/strong> for unions or type combinations.<\/li>\n<\/ul>\n\n\n\n
14) What are namespaces?<\/strong><\/p>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\nNamespaces<\/strong> provide a way to organize code by grouping related functionalities under a single name. They are primarily used to avoid global namespace pollution<\/strong> and can help manage large applications by logically grouping types, functions, and variables.<\/p>\n\n\n\nTypeScript namespaces use the namespace keyword, and internal members are encapsulated, reducing the risk of naming conflicts.<\/p>\n\n\n\n
Example<\/strong>:<\/p>\n\n\n\nnamespace Utilities {\n export function log(message: string): void {\n console.log(message);\n }\n}\n\nUtilities.log(\"Hello, World!\");<\/code><\/pre>\n\n\n\nKey Concepts<\/strong>:<\/p>\n\n\n\n\n- Encapsulation<\/strong>: Namespaces prevent code from polluting the global scope by keeping related code together.<\/li>\n\n\n\n
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