Summary of some common TypeScript interview questions

introduction

TypeScript is an open source, cross-platform programming language developed by Microsoft. It is a superset of JavaScript that adds static type systems and other advanced features to JavaScript. With the widespread application of TypeScript in the field of front-end development, mastering TypeScript has become one of the essential skills for many developers. This article will organize a series of common TypeScript interview questions to help developers preparing for the interview review and consolidate their knowledge.

1. TypeScript Basics

1.1 What is TypeScript?

• TypeScript is a statically typed, object-oriented programming language that can be compiled into pure JavaScript code.
• It is a superset of JavaScript, meaning that any valid JavaScript code is also valid TypeScript code.

1.2 What is the difference between TypeScript and JavaScript?

• TypeScript adds a static type system that can catch type errors during the compilation phase.
• TypeScript supports object-oriented programming concepts such as classes, interfaces, and enumerations.
• TypeScript provides more powerful tool support, such as automatic completion, intelligent perception and other functions.

1.3 How to install TypeScript?

• Install TypeScript via npm:
• bash

• Dark version

  npm install -g typescript

1.4 How to compile TypeScript?

• Use the tsc command to compile TypeScript files:

  Dark version

  tsc 

2. Types and Interfaces

2.1 What are the basic types in TypeScript?

• string, number, boolean, null, undefined, void, never, any, unknown。

2.2 How to define union type and cross type?

• Union Type:use|Symbols represent one of many types.

  Dark version

  let value: string | number;

• Cross type:use&Symbols represent combinations of multiple types.

  Dark version

  type Person = {
      name: string;
  };
  
  type Developer = {
      skill: string;
  };
  
  type DevPerson = Person & Developer;

2.3 What is the difference between interface and type alias?

• interface(Interface) is used to describe the shape of an object, which can be expanded and merged.

  Dark version

  interface Person {
      name: string;
      age: number;
  }

• Type alias(Type Alias) is used to alias the type, making it more flexible.

  Dark version

  type Person = {
      name: string;
      age: number;
  };

2.4 How to implement generics?

• use<T>Define generic type parameters.

  Dark version

  function identity<T>(arg: T): T {
      return arg;
  }

3. Advanced Type

3.1 How to define read-only attributes?

• usereadonlyKeyword definitions cannot be modified attributes.

  Dark version

  interface Person {
      readonly id: number;
      name: string;
  }

3.2 How to use condition types?

• Conditional types allow different types to be selected based on the results of type inference.

  Dark version

  type TypeName<T> =
      T extends string ? "string" :
      T extends number ? "number" :
      T extends boolean ? "boolean" :
      "unknown";

3.3 How to use mapping types?

• Mapping types allow new types to be created based on existing types.

  Dark version

  type Readonly<T> = {
      readonly [P in keyof T]: T[P];
  };

4. Classes and modules

4.1 How to define a class?

• useclassKeyword definition class.

  Dark version

  class Person {
      constructor(public name: string, public age: number) {}
      
      greet() {
          (`Hello, my name is ${}.`);
      }
  }

4.2 How to implement inheritance?

• useextendsKeyword inheritance.

  Dark version

  class Employee extends Person {
      constructor(name: string, age: number, public position: string) {
          super(name, age);
      }
      
      work() {
          (`${} is working.`);
      }
  }

4.3 How to use modules?

• useexportandimportKeyword import and export modules.

  Dark version

  // 
  export class Person {
      constructor(public name: string, public age: number) {}
  }
  
  // 
  import { Person } from './person';
  const person = new Person('Alice', 30);

5. Practical Tips

5.1 How to use type assertions?

• Type assertions allow you to "tell" the compiler the type of a value in TypeScript.

  Dark version

  const value: any = 'hello';
  const strLength: number = (value as string).length;

5.2 How to use type protection?

• useinstanceofKeyword or custom type protection function.

  Dark version

  function isString(value: any): value is string {
      return typeof value === 'string';
  }

5.3 How to use a decorator?

• A decorator is a special type of declaration that can be used to modify the behavior of a class.

  Dark version

  function log(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
      const originalMethod = ;
       = function (...args: any[]) {
          (`Calling "${propertyKey}" with`, args);
          return (this, args);
      };
  }
  
  class Calculator {
      @log
      add(a: number, b: number) {
          return a + b;
      }
  }

6. Object-Oriented Programming

6.1 How to use abstract classes?

• useabstractKeyword definition abstract class.

  Dark version

  abstract class Animal {
      abstract makeSound(): void;
  }
  
  class Dog extends Animal {
      makeSound() {
          ('Woof!');
      }
  }

6.2 How to use interface inheritance?

• useextendsKeyword inheritance interface.

  Dark version

  interface Shape {
      color: string;
  }
  
  interface Circle extends Shape {
      radius: number;
  }

7. TypeScript integration with other frameworks/libraries

7.1 How to use TypeScript in React?

• Defines the props and state types of the component.

  Dark version

  interface Props {
      name: string;
  }
  
  interface State {
      count: number;
  }
  
  class Greeting extends <Props, State> {
      state = { count: 0 };
      
      render() {
          return (
              <div>
                  Hello, {}!
                  Clicked {} times
              </div>
          );
      }
  }

7.2 How to use TypeScript in Angular?

• Use TypeScript's type system to define components and services.

  Dark version

  import { Component } from '@angular/core';
  
  @Component({
      selector: 'app-root',
      template: `
          <h1>{{ title }}</h1>
      `,
  })
  export class AppComponent {
      title = 'Angular App';
  }

8. Best Practices

8.1 How to avoid type errors?

• Use strict type checking.

  Dark version

  tsc --strict

• useneverType represents a path that never happens.

  Dark version

  function throwError(message: string): never {
      throw new Error(message);
  }

8.2 How to write maintainable code?

• Use interfaces and type alias to define clear data structures.
• Follow the principle of single responsibility.
• Use TypeScript's type system to reduce runtime errors.

in conclusion

Mastering the basics and advanced features of TypeScript is very important to becoming a qualified front-end developer. This article summarizes a series of common TypeScript interview questions, hoping to help developers prepare for interviews better, and at the same time deepen their understanding and application capabilities of TypeScript. If you have any questions or need further assistance, feel free to ask!

This is the end of this article about some common TypeScript interview questions. For more related TypeScript interview questions, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!