class AppError extends Error{
    constructor(message,statusCode){
        super(message)
        this.statusCode = statusCode
    }
}

AND

class AppError extends Error{
    constructor(message,statusCode){
        super(message)
        this.message=message
        this.statusCode = statusCode
    }
}

AND

class AppError{
    constructor(message,statusCode){
        this.message = message
        this.statusCode = statusCode
    }
}

I am woking on nodeJs project using mongo.During error handling I created this class but not understading difference between these.AND which is best way? does it matter if I extend to error class or not and direct assign message property? Most importantly. When I print object created using 1st class, why message property is missing ? Though when I print it explicitly (for eg. err.message) value is shown

CodePudding user response：

class Error {
    constructor(message) {
        this.message = message
    }
}

class AppError extends Error{
    constructor(message,statusCode){
        super(message) // This calls the constructor of the parent 
        this.statusCode = statusCode
    }
}

// AND

class AppError extends Error{
    constructor(message,statusCode){
        super(message) // This calls the parent constructor
        this.message=message // This ovverrides the previous line
        this.statusCode = statusCode
    }
}

// AND

class AppError{
    constructor(message,statusCode){
        this.message = message // This is just without the extended class
        this.statusCode = statusCode
    }
}

Another example: This shows you that the parent constructor is called, but you are missing chicken and food

class Error {
    constructor(message, chicken, food) {
        this.message = message
        this.chicken = chicken
        this.food = food
    }
}

class AppError extends Error {
    constructor(message, statusCode) {
        super(message)
        this.statusCode = statusCode
    }
}

let x = new AppError("Message", "Errorcode")
console.log(x)

To reduce redundant code and you have a lots of class parameters it could look like this:

class Animal {
    constructor(price, size, age) {
        this.price = price
        this.size = size
        this.age = age
    }
}

class Cat extends Animal {
    constructor(cattype, price, size, age) {
        super(price, size, age) // This is way shorter than repeating what is written in the Animal class
        this.cattype = cattype
    }
}

let x = new Cat("weirdtype", "500Euros", "BigSize", "OldAge")
console.log(x)

CodePudding user response：

• The class AppError extends (inherit) from the Error class
• That means AppError's this context includes the properties and methods defined in the Error class, plus whatever properties and methods AppError defines for itself.
• Call the super(arguments) in the child class constructor to invoke the parent class constructor

Let them know that no question is too small or too strange to be asked :)

Js is interesting try this book

https://javascript.info/

https://eloquentjavascript.net/ :)