javascript - 位于 for-each 中的记录器的引用错误

Question

我正在使用 javascript 并有以下类:

const Product = require('../models').Product

class ProductService {

    constructor(log) {
        this.logger = log
    }

    async generateIssuerRatingChangeContent(id, helperService, productService) {
        let products
        try {
            products = await productService.getproductByid(id)
        } catch (error) {
            this.logger.error(error)
        }
        this.logger.info("Get #products: " + products.length)

        let contentArr = []
        this.logger.info("##############Start to clean products##############")
        products.forEach(async function (item) {

            const res = {
               //...
            }

            let resultString = await helperService.stringCleaner(res)
            contentArr.push(resultString)
            this.logger.info(resultString); // <--- HERE I get an ReferenceError!!!
            console.log(resultString);
            this.logger.info("#####################-DONE WITH " + item.id + "-#####################");
        });
        await helperService.writeContentToFile(contentArr)

    }
}

module.exports = {
    ProductService
};

我目前在 for-each 循环内的 logger 实例上遇到错误。

为什么我无法使用 this 访问它？

感谢您的回复!

Answer 1

当您使用 function 关键字定义回调时，上下文会发生变化。相反，请尝试使用箭头函数，它将继承父上下文 (this)。

const Product = require('../models').Product

class ProductService {

    constructor(log) {
        this.logger = log
    }

    async generateIssuerRatingChangeContent(id, helperService, productService) {
        let products
        try {
            products = await productService.getproductByid(id)
        } catch (error) {
            this.logger.error(error)
        }
        this.logger.info("Get #products: " + products.length)

        let contentArr = []
        this.logger.info("##############Start to clean products##############")
        products.forEach(async (item) => {

            const res = {
               //...
            }

            let resultString = await helperService.stringCleaner(res)
            contentArr.push(resultString)
            this.logger.info(resultString); // <--- HERE I get an ReferenceError!!!
            console.log(resultString);
            this.logger.info("#####################-DONE WITH " + item.id + "-#####################");
        });
        await helperService.writeContentToFile(contentArr)

    }
}

module.exports = {
    ProductService
};