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TypeScript – Decorators

Author: admin - Posted: 27/10/22 - Update: 12/11/22

import "reflect-metadata";
const formatMetadataKey = Symbol("format");
const requiredMetadataKey = Symbol("required");

// Class Decorator
const Entity = (options: { stdName?: string, tblName?: string }) => (target: Function & typeof BaseEntities) => {
    target.prototype.studentName = options.stdName
    target.tableName = options.tblName
}

// Property Decorator
const CreatedAt = (options: { format?: string }) => (target: Object, propertyName: string) => {
    let time = new Date();
    const getter = () => {
        let value: string | number
        if (options.format === 'getTime') {
            value = time.getTime()
        }
        if (options.format === 'toLocaleString') {
            value = time.toLocaleString()
        }
        return value
    }
    const setter = (value: string | number) => {
        console.log("Start edit to:", value)
        time = new Date(value)
    }
    Object.defineProperty(target, propertyName, { get: getter, set: setter })
}

// Method Decorator
const PrintJSON = (options: { indent: number }) => (target: Object, propertyKey: string, propertyDescriptor: PropertyDescriptor) => {
    const originMethod = propertyDescriptor.value
    propertyDescriptor.value = function (...args: any[]) {
        // const result = originMethod.apply(this, args)
        const result = originMethod.call(this, ...args)
        result.create_at = this.create_at
        return JSON.stringify(result, null, options.indent)
    }
    return propertyDescriptor
}

// Params Decorator
const ConvertTime = (options: { format: string }) => (target: Object, propertyKey: string, parameterIndex: number) => {
    let existingRequiredParameters: number[] = Reflect.getOwnMetadata(requiredMetadataKey, target, propertyKey) || [];
    existingRequiredParameters.push(parameterIndex);
    Reflect.defineMetadata(requiredMetadataKey, existingRequiredParameters, target, propertyKey);
    console.log({ target, propertyKey, parameterIndex, options, requiredMetadataKey, existingRequiredParameters })
    // Loằng ngoằng, cái Reflect này chưa hiểu
}

class BaseEntities {
    static tableName: string
    studentName: string
}

@Entity({ stdName: "Ngô Nhật Dương", tblName: "table_student" })
class StudentEntities extends BaseEntities {
    @CreatedAt({ format: 'getTime' })
    create_at: string | number

    @PrintJSON({ indent: 4 })
    printData(@ConvertTime({ format: 'getTime' }) printDate: string) {
        return { studentName: this.studentName, printDate }
    }
}

const student1 = new StudentEntities()
console.log("Entity infomation:", student1.studentName, StudentEntities.tableName)
console.log("Student infomation: create_at =", student1.create_at)
student1.create_at = '11/12/2005, 10:31:23 PM'
console.log("Student after edit: create_at =", student1.create_at)
console.log("Student printData:", student1.printData(new Date().toString()))

import "reflect-metadata";

const formatMetadataKey = Symbol("format");

const requiredMetadataKey = Symbol("required");

// Class Decorator

const Entity = (options: { stdName?: string, tblName?: string }) => (target: Function & typeof BaseEntities) => {

target.prototype.studentName = options.stdName

target.tableName = options.tblName

}

// Property Decorator

const CreatedAt = (options: { format?: string }) => (target: Object, propertyName: string) => {

let time = new Date();

const getter = () => {

let value: string | number

if (options.format === 'getTime') {

value = time.getTime()

}

if (options.format === 'toLocaleString') {

value = time.toLocaleString()

}

return value

}

const setter = (value: string | number) => {

console.log("Start edit to:", value)

time = new Date(value)

}

Object.defineProperty(target, propertyName, { get: getter, set: setter })

}

// Method Decorator

const PrintJSON = (options: { indent: number }) => (target: Object, propertyKey: string, propertyDescriptor: PropertyDescriptor) => {

const originMethod = propertyDescriptor.value

propertyDescriptor.value = function (...args: any[]) {

// const result = originMethod.apply(this, args)

const result = originMethod.call(this, ...args)

result.create_at = this.create_at

return JSON.stringify(result, null, options.indent)

}

return propertyDescriptor

}

// Params Decorator

const ConvertTime = (options: { format: string }) => (target: Object, propertyKey: string, parameterIndex: number) => {

let existingRequiredParameters: number[] = Reflect.getOwnMetadata(requiredMetadataKey, target, propertyKey) || [];

existingRequiredParameters.push(parameterIndex);

Reflect.defineMetadata(requiredMetadataKey, existingRequiredParameters, target, propertyKey);

console.log({ target, propertyKey, parameterIndex, options, requiredMetadataKey, existingRequiredParameters })

// Loằng ngoằng, cái Reflect này chưa hiểu

}

class BaseEntities {

static tableName: string

studentName: string

}

@Entity({ stdName: "Ngô Nhật Dương", tblName: "table_student" })

class StudentEntities extends BaseEntities {

@CreatedAt({ format: 'getTime' })

create_at: string | number

@PrintJSON({ indent: 4 })

printData(@ConvertTime({ format: 'getTime' }) printDate: string) {

return { studentName: this.studentName, printDate }

}

const student1 = new StudentEntities()

console.log("Entity infomation:", student1.studentName, StudentEntities.tableName)

console.log("Student infomation: create_at =", student1.create_at)

student1.create_at = '11/12/2005, 10:31:23 PM'

console.log("Student after edit: create_at =", student1.create_at)

console.log("Student printData:", student1.printData(new Date().toString()))

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