JavaScript_code_snippets/my_promise_implement.html at master · dendoink/JavaScript_code_snippets · GitHub

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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<script>
    const PENDING = new Symbol()
    const FULFILLED = new Symbol()
    const REJECTED = new Symbol()

    class MyPromise {
        // excutor 初始化 promise 时定义的回调函数
        constructor(excutor) {
            this.status = PENDING
            // FULFILLED 状态下有 value
            this.value = undefined
            // REJECTED 状态下有 reason
            this.reason = undefined
            // 这两个函数是调动 then 方法的参数
            this.onFulfilled = () => {

            }
            this.onRejected = () => { }

            this.resolve = (value) => {
                if (this.status === PENDING) {
                    this.status = FULFILLED
                    this.value = value
                }

            }
            this.reject = (reason) => {
                this.status = REJECTED
            }
            try {
                excutor(resolve, reject)
            } catch (error) {

            }
        }
        then(onFulfilled, onRejected) {
            return new MyPromise()
        }

    }
</script>

</html>