SOURCE

class MyPromise {
    constructor(fn) {
        this.callbacks = [];
        this.value = undefined;
        this.state = 'pending'
        fn(this.resolve.bind(this))
    }
    resolve(value) {
        this.state = 'fulfilled'
        this.value = value
        this.callbacks.forEach((callback) => { this.hande(callback) })
    }
    async hande(callback) {
        const { onFulfilled, resolve } = callback;
        let res=this.value;
        if (this.state == 'pending') {
            this.callbacks.push(callback)
            return
        }
        if (onFulfilled) {
            console.log(111)
            res = await onFulfilled(this.value)
            console.log(222)
        }
            console.log(3333)
        resolve(res)
        // if (!onFulfilled) {
        //     resolve(this.value)
        //     return;
        // }
        // const res = await onFulfilled(this.value)
        // resolve(res)
    }
    then(onFulfilled = null) {
        return new MyPromise(resolve => {
            this.hande({
                onFulfilled,
                resolve,
            })
        })

    }
}
let p = new MyPromise((resolve) => {
    // resolve(1)
    setTimeout(() => { resolve(1) }, 1_000)
}).then((r) => {
    console.log(`1:${r}`)
    return r
})
    .then((r) => new MyPromise((resove, reject) => {
        setTimeout(() => {
            resove(2)
            console.log(`2:${r}`)
        }, 1_000 * 4)
    })
    )
    .then((r) => {
        console.log(`3:${r}`)
        return r
    })
    .then((r) => {
        console.log(`4:${r}`)
        return r
    })
    .then((r) => {
        console.log(`5:${r}`)
    })