Declaration of custom object or type in Node.js

In Node.js, when you want to assign one object to another that is declared by a custom type or class, you typically need to ensure compatibility between the source object's structure and the target class's expectations. Here's a breakdown:

Scenario 1: Assigning Plain Objects to Class Instances

If you have a custom class and want to assign properties from a plain object to an instance of that class, you can use one of the following methods:

Example:

class CustomType {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }
}

// Plain object
const plainObject = { name: "John", age: 30 };

// Assign using Object.assign()
const customInstance = new CustomType();
Object.assign(customInstance, plainObject);

console.log(customInstance instanceof CustomType); // true
console.log(customInstance); // CustomType { name: 'John', age: 30 }

Scenario 2: Using a Constructor

You can modify your class to accept an object in the constructor for direct assignment:

class CustomType {
  constructor({ name, age }) {
    this.name = name;
    this.age = age;
  }
}

// Plain object
const plainObject = { name: "John", age: 30 };

// Create an instance
const customInstance = new CustomType(plainObject);

console.log(customInstance instanceof CustomType); // true
console.log(customInstance); // CustomType { name: 'John', age: 30 }

Scenario 3: Validation or Transformation

If you need to validate or transform the input object before assigning, you can implement a custom method:

class CustomType {
  constructor() {
    this.name = "";
    this.age = 0;
  }

  assignFromObject(obj) {
    if (obj.name && typeof obj.name === "string") {
      this.name = obj.name;
    }
    if (obj.age && typeof obj.age === "number") {
      this.age = obj.age;
    }
  }
}

// Plain object
const plainObject = { name: "John", age: 30 };

// Assign using the custom method
const customInstance = new CustomType();
customInstance.assignFromObject(plainObject);

console.log(customInstance instanceof CustomType); // true
console.log(customInstance); // CustomType { name: 'John', age: 30 }

Scenario 4: Using Static Methods

A static method can return a new instance based on a plain object:

class CustomType {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  static fromObject(obj) {
    return new CustomType(obj.name, obj.age);
  }
}

// Plain object
const plainObject = { name: "John", age: 30 };

// Create instance using static method
const customInstance = CustomType.fromObject(plainObject);

console.log(customInstance instanceof CustomType); // true
console.log(customInstance); // CustomType { name: 'John', age: 30 }

Key Considerations

  • Validation: Ensure the source object has the expected properties and types.
  • Prototypes: Direct assignment (Object.assign) won't copy methods or prototype chain relationships.
  • Deep Copy: Use libraries like lodash if the object has nested structures that need cloning.

Choose the approach based on your specific needs for validation, transformation, and maintainability.

댓글

이 블로그의 인기 게시물

Install and run an FTP server using Docker

Using the MinIO API via curl

PYTHONPATH, Python 모듈 환경설정

Elasticsearch Ingest API

오늘의 문장2

How to checkout branch of remote git, 깃 리모트 브랜치 체크아웃

Fundamentals of English Grammar #1

To switch to a specific tag in a Git repository

You can use Sublime Text from the command line by utilizing the subl command

티베트-버마어파 와 한어파(중국어파)의 어순 비교