JavaScript 异步迭代器组合器：现代应用的流转换

            
const asyncIterable = {
  [Symbol.asyncIterator]() {
    let i = 0;
    return {
      async next() {
        await new Promise(resolve => setTimeout(resolve, 100)); // Simulate asynchronous operation
        if (i < 3) {
          return { value: i++, done: false };
        } else {
          return { value: undefined, done: true };
        }
      }
    };
  }
};

(async () => {
  for await (const value of asyncIterable) {
    console.log(value); // Output: 0, 1, 2
  }
})();

            

              
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async function* asyncGenerator() {
  let i = 0;
  while (i < 3) {
    await new Promise(resolve => setTimeout(resolve, 100));
    yield i++;
  }
}

(async () => {
  for await (const value of asyncGenerator()) {
    console.log(value); // Output: 0, 1, 2
  }
})();

            

              
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async function* map(iterable, fn) {
  for await (const value of iterable) {
    yield await fn(value);
  }
}

// Example:
async function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
}

async function square(x) {
  await new Promise(resolve => setTimeout(resolve, 50)); // Simulate async operation
  return x * x;
}

(async () => {
  const squaredNumbers = map(numberGenerator(), square);
  for await (const value of squaredNumbers) {
    console.log(value); // Output: 1, 4, 9 (with delays)
  }
})();

            

              
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async function* filter(iterable, predicate) {
  for await (const value of iterable) {
    if (await predicate(value)) {
      yield value;
    }
  }
}

// Example:
async function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
  yield 5;
}

async function isEven(x) {
  await new Promise(resolve => setTimeout(resolve, 50));
  return x % 2 === 0;
}

(async () => {
  const evenNumbers = filter(numberGenerator(), isEven);
  for await (const value of evenNumbers) {
    console.log(value); // Output: 2, 4 (with delays)
  }
})();

            

              
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async function* take(iterable, n) {
  let i = 0;
  for await (const value of iterable) {
    if (i < n) {
      yield value;
      i++;
    } else {
      return;
    }
  }
}

// Example:
async function* infiniteNumberGenerator() {
  let i = 0;
  while (true) {
    await new Promise(resolve => setTimeout(resolve, 50));
    yield i++;
  }
}

(async () => {
  const firstFiveNumbers = take(infiniteNumberGenerator(), 5);
  for await (const value of firstFiveNumbers) {
    console.log(value); // Output: 0, 1, 2, 3, 4 (with delays)
  }
})();

            

              
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async function* drop(iterable, n) {
  let i = 0;
  for await (const value of iterable) {
    if (i >= n) {
      yield value;
    } else {
      i++;
    }
  }
}

// Example:
async function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
  yield 5;
}

(async () => {
  const remainingNumbers = drop(numberGenerator(), 2);
  for await (const value of remainingNumbers) {
    console.log(value); // Output: 3, 4, 5
  }
})();

            

              
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async function reduce(iterable, reducer, initialValue) {
  let accumulator = initialValue;
  for await (const value of iterable) {
    accumulator = await reducer(accumulator, value);
  }
  return accumulator;
}

// Example:
async function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
  yield 5;
}

async function sum(a, b) {
  await new Promise(resolve => setTimeout(resolve, 50));
  return a + b;
}

(async () => {
  const total = await reduce(numberGenerator(), sum, 0);
  console.log(total); // Output: 15 (after delays)
})();

            

              
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async function* flatMap(iterable, fn) {
  for await (const value of iterable) {
    const innerIterable = await fn(value);
    for await (const innerValue of innerIterable) {
      yield innerValue;
    }
  }
}

// Example:
async function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
}

async function* duplicate(x) {
  await new Promise(resolve => setTimeout(resolve, 50));
  yield x;
  yield x;
}

(async () => {
  const duplicatedNumbers = flatMap(numberGenerator(), duplicate);
  for await (const value of duplicatedNumbers) {
    console.log(value); // Output: 1, 1, 2, 2, 3, 3 (with delays)
  }
})();

            

              
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async function forEach(iterable, fn) {
  for await (const value of iterable) {
    await fn(value);
  }
}

// Example:
async function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
}

async function logNumber(x) {
  await new Promise(resolve => setTimeout(resolve, 50));
  console.log("Processing:", x);
}

(async () => {
  await forEach(numberGenerator(), logNumber);
  console.log("Done processing.");
  // Output: Processing: 1, Processing: 2, Processing: 3, Done processing. (with delays)
})();

            

              
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async function toArray(iterable) {
  const result = [];
  for await (const value of iterable) {
    result.push(value);
  }
  return result;
}

// Example:
async function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
}

(async () => {
  const numbersArray = await toArray(numberGenerator());
  console.log(numbersArray); // Output: [1, 2, 3]
})();

            

              
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async function* numberGenerator() {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
  yield 5;
  yield 6;
  yield 7;
  yield 8;
  yield 9;
  yield 10;
}

async function isEven(x) {
  return x % 2 === 0;
}

async function square(x) {
  return x * x;
}

async function* filter(iterable, predicate) {
    for await (const value of iterable) {
        if (await predicate(value)) {
            yield value;
        }
    }
}

async function* map(iterable, fn) {
    for await (const value of iterable) {
        yield await fn(value);
    }
}

async function* take(iterable, n) {
    let i = 0;
    for await (const value of iterable) {
        if (i < n) {
            yield value;
            i++;
        } else {
            return;
        }
    }
}

(async () => {
  const pipeline = take(map(filter(numberGenerator(), isEven), square), 3);
  for await (const value of pipeline) {
    console.log(value); // Output: 4, 16, 36
  }
})();

            

              
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async function* stockDataStream() {
  // Simulate a stream of stock data from different exchanges
  const exchanges = ['NYSE', 'NASDAQ', 'LSE', 'HKEX'];
  const symbols = ['AAPL', 'MSFT', 'GOOG', 'TSLA', 'AMZN', 'BABA'];

  while (true) {
    await new Promise(resolve => setTimeout(resolve, Math.random() * 500));
    const exchange = exchanges[Math.floor(Math.random() * exchanges.length)];
    const symbol = symbols[Math.floor(Math.random() * symbols.length)];
    const price = Math.random() * 2000;

    yield { exchange, symbol, price };
  }
}

async function isNYSE(stock) {
  return stock.exchange === 'NYSE';
}

async function* filter(iterable, predicate) {
  for await (const value of iterable) {
    if (await predicate(value)) {
      yield value;
    }
  }
}


async function toLatestPrices(iterable) {
    const latestPrices = {};
    for await (const stock of iterable) {
        latestPrices[stock.symbol] = stock.price;
    }
    return latestPrices;
}

async function forEach(iterable, fn) {
  for await (const value of iterable) {
    await fn(value);
  }
}


(async () => {
  const nyseStocks = filter(stockDataStream(), isNYSE);
  const updateUI = async (stock) => {
       //Simulate UI update
       console.log(`UI updated with : ${JSON.stringify(stock)}`)
       await new Promise(resolve => setTimeout(resolve, Math.random() * 100));
  }

  forEach(nyseStocks, updateUI);
})();


            

              
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