Js chain call problem

write a chained call as follows:

new Man("lan").sleep(3).eat("apple").sleep(3).eat("banana");

output:
hello, lan--> (pause 3s)-> lan eat apple-> (pause 3s)-> lan eat banana
my code is as follows:

class Man {
    constructor(name) {
        this.name = name;
        this.sayName();
    }
    sayName() {
        console.log("hi "+this.name);
    }
    sleep(time) {
        var self = this;
        new Promise((res, rej)=> {
            setTimeout(()=> {
                res("");
            }, time*1000)
        }).then(val=> {
            return self;
        });
    }
    eat(food) {
        console.log(this.name + "" + food);
        return this;
    }
}

new Man("").sleep(3).eat("").sleep(3).eat("");

the problem lies in the sleep node. Although promise is used, the this pointer cannot be returned in time, resulting in sleep (3). Eat (".") The Times mistakenly said that there was no eat function.

what should I do to solve this problem?

Chain-method promise javascript

Mar.03,2021

it is recommended to know the usage of promise.

    new Promise((res, rej)=> {
        setTimeout(()=> {
            res('');
        }, time*1000)
    }).then(val=> {
        return self;
    });

obviously your sleep has no action. If you want to use promise design pause, it is recommended that you create a simple process control and write a chain of then

class Man{
    constructor(name) {
        this.name = name;
        this.sayName();
        this.chain = Promise.resolve(this)
    }
    sayName() {
        console.log('hi '+this.name);
    }
    sleep(time) {
        this.chain = this.chain.then((v)=>{
            return new Promise((resolve,reject)=>{
                setTimeout(()=>{
                    resolve(v)
                },time*1000)
            })
        })
        return this;
    }
    eat(food) {
        this.chain = this.chain.then((v)=>{
            console.log(`eat ${food}`)
            return Promise.resolve(v)
        })
        return this
    }
}

you should not return this, that is, Man object, but should wrap another object and return

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