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JavaScript Promise? ??? ????? ??? ?????? ????? ???? ??.

??????? ??? Promise? ??? ???! Promise/A ??? ??? Promise? ??? ??? ????, ????, ????, ?? ??? ?? ? ?? ??? ???? ??? ?????.

?? ???? ???? ?? Promises/A ???? ?? ??? ?? ??? ??? ?????. ?? ?? ??? ??? ???? ?????. ??? ??? ??? ??? ????.

1. ??

1.1 'promise'? ? ??? ???? ??? ?? then ???? ?? ?? ?? ?????.

1.2 thenable'? then ???? ???? ?? ?? ?????.

1.3 '?'? ??? JavaScript ?(???? ??, Thenable ?? Promise ??)???.

1.4 '??'? throw ?? ???? ???? ????.

1.5 '??'? Promise? ??? ??? ???? ????.

2. ????

2.1 ?? ??

??? ??, ?? ?? ??? ? ?? ?? ? ???? ???.

2.1.1. ?? ?? ?? ??: ?

? ?? ?? ?? ??? ??? ? ????.

2.1.2. ???? ??: ?

? ?? ??? ???? ? ???.

? ?? ??? ?? ?????? ? ???.

2.1.3. ???? ??: ?

? ?? ??? ???? ? ???.

? ?? ? ?? ??? ??? ???.

2.2 then ???

Promise? ?? ?? ?? ??? ??? ????? ?? then ???? ???? ???.

Promise? then ???? ? ?? ??? ????:

promise.then(onFulfilled, onRejected);

2.2.1. onFulfilled ? onRejected? ?? ??? ?????: ?

? onFulfilled? ??? ??? ???? ???.

? onRejected? ??? ?? ?? ???? ???.

2.2.2. onFulfilled? ??? ??: ?

? Promise ?? ? ?? ??? ???? Promise? ??? ?? ???? ???.

? ??? ???? ??? ???? ? ???.

? ? ? ?? ???? ? ???.

2.2.3. onRejected? ??? ?? ?

? Promise? ??? ?? ???? ?? Promise? ??? ? ?? ??? ???? ???? ???.

? ??? ???? ?? ???? ? ???.

? ? ? ?? ???? ? ???.

2.2.4. ?? ???? ??? ??? ??? ??? ??? onFulfilled ?? onRejected? ???? ? ???. ?

2.2.5. onFulfilled ? onRejected? ??? ????? ???(?, ? ?? ??). ?

2.2.6. ?? ?? ??? Promise? ?? ?? ? ??? ? ????. ?

? ??? ???? ?? ?? onFulfilled ??? ?? ?? ???? ????? ???.

? ??? ???? ?? ?? ?? onRejected ??? ?? ?? ???? ????? ???.

2.2.7. ?? ?? ??? ???? ???. ?

promise.then(onFulfilled, onRejected);

? onFulfilled ?? onRejected? x ?? ???? ?? ?? ?? ?? [[Resolve]](promise2, x)? ?????. ?

? onFulfilled ?? onRejected?? ?? e? ???? promise2? e? ??? ????? ???. ?

? onFulfilled? ??? ??? promise1? ??? ?? promise2? promise1? ??? ??? ????? ???. ?

? onRejected? ??? ??? promise1? ??? ?? promise2? promise1? ?? ??? ????? ???. ?

??

JavaScript Promise? Promise? ??? ? ?? ???? ??? ??? ??? ?????.

promise2 = promise1.then(onFulfilled, onRejected);

new Promise(excecutor);

?? Promise/A ??? Promise? ??, ?? ?? ???? ??? ??? ????. ??? ???? ?? ????. ??? Promise ??? ?? ???? ??? JavaScript? ??? API? ????? ???. Promise ???? ? ?? ??? ??? ????.

const promise = new Promise((resolve, reject) => {
    // Runs some async or sync tasks
});

?? 2.1(?? ??)?? ??? ??, ?? ?? ??? ? ?? ?? ? ??? ??? ??? ???? ????. ?? ? ???? ?? ?? ????? ?????.

Promise? ????? ???? Promise? ?? ??? ?????? ? ???. ??? ??? ?? ?? Promise? ?? ???? ???? ???.

class YourPromise {
    constructor(executor) {
        this.state = 'pending';
        this.value = undefined;
        this.reason = undefined;

        const resolve = value => {
            if (this.state === 'pending') {
                this.state = 'fulfilled';
                this.value = value;
            }
        };

        const reject = reason => {
            if (this.state === 'pending') {
                this.state = 'rejected';
                this.reason = reason;
            }
        };

        try {
            executor(resolve, reject);  // The executor function being called immediately
        } catch (error) {
            reject(error);
        }
    }
}

????? ?? ??? ?? ???? ?? ?? ?? ??? ????? ????? ??? ??? ??? ????? ???.

const resolve = value => {
    if (this.state === 'pending') {
        this.state = 'fulfilled';
        this.value = value;
    }
};

const reject = reason => {
    if (this.state === 'pending') {
        this.state = 'rejected';
        this.reason = reason;
    }
};

??? ??? promise? ??????? ?? ????? ??? ??? ??? ?????.

this.state = 'pending';

YourPromise ???? ? ?? ??? ???? ???????.

Promise/A ??? ?? ?? ?? ??? then() ???? ???? ? ??? ???. ? ???? ???? Promise? ?? ?? ?? ??? ??? ???? ? ????. ??? ???????.

?? 2.2(then ???)??? Promise? ? ?? ??? ???? then() ???? ??? ??? ?????.

try {
    executor(resolve, reject);
} catch (error) {
    reject(error);
}

onFulfilled ? onRejected? ?? ??? ????? ??? ?? ????? ??, ??? ?? ??? ??? ??? ? ?? ??? ???? ???.

class YourPromise {
    constructor(executor) {
        // Implementation
    }

    then(onFulfilled, onRejected) {
        // Implementation
    }
}

?? ??? ????? ???? ?? ????? ? ??, ? ? ?? ???? ? ???. onFulfilled ? onRejected? ?? ?? ????? ??? ?? ?? ???? ???.

?? 2.2, 2.2.6, 2.2.7? ?? Promise?? then() ???? ??? ?? then() ???? ?? ? ??? ? ??? ??? ???? ??? ?? ? ? ????. ??:

promise.then(onFulfilled, onRejected);

???? ?? ?? ??? ???? ??? ??? ????. ??? ??? ???? Promise ??? ?????.

promise2 = promise1.then(onFulfilled, onRejected);

Executor ?? ??? ??? ???? onFulfilled ??? ???? ?? ??? ?????. ????? ??? ???? onRejected ??? ???? ?? ??? ?? ?????.

?? ??? Promise? ?? ?? ??? ?? onFulfilled ? onRejected ??? ??? ???? ??????. ??? ?? ??? ????? ???? ?????.

new Promise(excecutor);

?????. ??? then() ???? ???? Promise ???? ? ?? ?????.

const promise = new Promise((resolve, reject) => {
    // Runs some async or sync tasks
});

????? ??? ???? ?? ???? onFulfilledCallbacks ? onRejectedCallbacks?? ? ??? ?????. ??? ???? Promise? ?? ?? ?? then() ??? ?? ???? ???? Promise? ????? ??? ? ?????.

Promise ???? ???? ???.

class YourPromise {
    constructor(executor) {
        this.state = 'pending';
        this.value = undefined;
        this.reason = undefined;

        const resolve = value => {
            if (this.state === 'pending') {
                this.state = 'fulfilled';
                this.value = value;
            }
        };

        const reject = reason => {
            if (this.state === 'pending') {
                this.state = 'rejected';
                this.reason = reason;
            }
        };

        try {
            executor(resolve, reject);  // The executor function being called immediately
        } catch (error) {
            reject(error);
        }
    }
}

??? ?? ????? ???.

const resolve = value => {
    if (this.state === 'pending') {
        this.state = 'fulfilled';
        this.value = value;
    }
};

const reject = reason => {
    if (this.state === 'pending') {
        this.state = 'rejected';
        this.reason = reason;
    }
};

??, ?? ???? ????:

this.state = 'pending';

??? ?? ? ????:

try {
    executor(resolve, reject);
} catch (error) {
    reject(error);
}

??:

class YourPromise {
    constructor(executor) {
        // Implementation
    }

    then(onFulfilled, onRejected) {
        // Implementation
    }
}

??? ??? then()? ??? ? YourPromise ????? ?? ????? ??? ?? then() ???? ??? ???? ??? ????. ?? ?? ??? ?? ?? ?? ?? then() ???? ?? ??? ?? ???? ?? ???? ???? ???? ????. ??? ?? ?? ?? ??? ?????. ?? ??????:

? ??? '?? ??'??? ??? ?? ?????.

? promise.then()? ???? ??? ?? ??????? onFulfilled ??? ?? ???? ?? ???? ???? ?? ?? ?????.

??? ?? 2.2.4? ?????. ? ??? Promise? ?? ????? ??? ???? then() ??(onFulfilled ?? onRejected)? ?????? ????? ?????. ?, ?? ?? ??? ??? ???? ??? ??(?: ??? ?? ?? ???? ?? ???)? ??? ??? ??? ????? ? ???.

? ??? ? ??????

? ??? Promise/A ???? ?? ??? ?? ? ?????. ??? ???? ?????.

? Promise? ?? ?????? ?? then() ??? ??? ??? ?? ??? ???? ????.

? ? ??? setTimeout ?? process.nextTick? ?? JavaScript? ?? ??? API ??? ?????.

??? ?? ??? ? ????

?? setTimeout ?? setImmediate? ?? ??? ?? ?????? queueMicrotask ?? process.nextTick? ?? ???? ?? ????? ???? ??? ? ????. ???? ???? ??? ?? ?? ?? ??? ????? ??? ?? JavaScript ?? ????? ??? ?? ???? ?????.

? ??? ????? ??? ?? ????? ??? ???? ?? ??(onFulfilled ?? onRejected)? queueMicrotask? ???? ?????? ????? ?? ???. ??? ??? ??? ????.

promise.then(onFulfilled, onRejected);

?? ?? ??? ??? ?? ?????. ??? ?? ??? ?????.

promise2 = promise1.then(onFulfilled, onRejected);

?????.

?? then()? ??? ??? ???? ?? ???? ?? ????? ???? ??? ??? ?????? ???? ???? ???. JavaScript? ???? ??? ??? ????? ? ??? ??? ???? ?? ??????.

??? ?????? ? ????? ?? Promises/A ??? ??? ????? ? ?? ???? ?? ??? ??? ??? ? ? ????.

???? ????? ???? ????? ????! ??? ??????.

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? ??? JavaScript? ??? Promise ???? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!