异步/等待班级:意外的令牌``this'

Question

我正在尝试异步/等待，我不明白为什么这行：

resolvedValue = await this.tryToSolve()

给我这个错误：

意外的令牌这个

class Test {
	constructor() {
		this.method = 0
		this.checkLink()
	}
	async checkLink() {
		return new Promise((resolve, reject) => {
			let resolvedValue
			for (let i = 0; i < 3; i++) {
				this.method = i
				resolvedValue = await this.tryToSolve()
				if (resolvedValue) break
			}
			console.log(`Method ${this.method} did the trick.`);
			resolve(resolvedValue)
		})
	}
	tryToSolve() {
		return new Promise((resolve, reject) => { // Resolves if this.method==1
			console.log(`Trying to solve with method ${this.method}...`);
			setTimeout(() => {
				resolve(!!this.method ? `http://www${this.method}.someurl.com` : false)
			}, 1000)
		})
	}
}
const test = new Test()

有人知道正确的语法将异步方法的结果存储在变量中吗？

预先感谢。

Answer 1

要使事情变得简单，它发生了，因为当您创建诺言时，在其'构造函数中，您通过箭头函数，其中包含 await调用。您必须始终将async关键字放在声明函数之前，其中包含await。

所以，而不是这样做

async checkLink() {
    return new Promise((resolve, reject) => {
        let resolvedValue
        for (let i = 0; i < 3; i++) {
            this.method = i
            resolvedValue = await this.tryToSolve()
            if (resolvedValue) break
        }
        console.log(`Method ${this.method} did the trick.`);
        resolve(resolvedValue)
    })
}

这样做

checkLink() {
    return new Promise(async (resolve, reject) => {
        let resolvedValue
        for (let i = 0; i < 3; i++) {
            this.method = i
            resolvedValue = await this.tryToSolve()
            if (resolvedValue) break
        }
        console.log(`Method ${this.method} did the trick.`);
        resolve(resolvedValue)
    })
}

更多信息：https：//ponyfoo.com/articles/understanding-javascript-async-await#using-async-await

Answer 2

在 await周围丢下 new Promise！您只需要

async checkLink() {
    let resolvedValue
    for (let i = 0; i < 3; i++) {
        this.method = i
        resolvedValue = await this.tryToSolve()
        if (resolvedValue) break
    }
    console.log(`Method ${this.method} did the trick.`);
    return resolvedValue;
}

或更简单

async checkLink() {
    for (let i = 0; i < 3; i++) {
        const value = await this.tryToSolve()
        if (value) {
            console.log(`Method ${i} did the trick.`);
            return value;
        }
    }
}