promise.html

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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>

const isFunc = func => typeof func === 'function'
    const PENDING = 'PENDING'
    const FULFILLED = 'FULFILLED'
    const REJECTED = 'REJECTED'
    class Promises {
        constructor(promiseFunc) {
            if (!isFunc(promiseFunc)) {
                throw new Error('请输入函数')
            }
            this.state = PENDING
            this.value = undefined
            this.fulfilledQueues = []
            this.rejectedQueues = []
            promiseFunc(this.resolve.bind(this), this.reject.bind(this))
        }
        resolve(value) {
            if (this.state !== PENDING) return
            this.state = FULFILLED
            this.value = value
        }
        reject(value) {
            if (this.state !== PENDING) return
            this.state = REJECTED
            this.value = value
        }

        then(success, error) {
            const { state, value } = this
            if (state === FULFILLED) {
                success(value)
            } else if (state === REJECTED) {
                error(value)
            }


            return new Promises((onFulfilledNext, onRejectedNext) => {
                let fulfilled = value => {

                }
            })

        }
    }

    const promise = new Promises((resolve, reject) => {
        resolve(111)


    })
    promise.then(res => {
        console.log('res', res)
    })


</script>
</html>