JavaScript execute asynchronous functions in Parallel with count and Promise All In One

JavaScript execute asynchronous functions in Parallel with count and Promise All In One

JavaScript 使用 count 和 Promise 并行执行异步函数

errors

function promiseAll<T>(functions: Fn<T>[]): Promise<T[]> {
  return new Promise((resolve, reject) => {
    let temp = [];
    for(let [i, func] of Object.entries(functions)) {
      console.log(`✅ i =`, i);
      console.log(`✅ func =`, func);
      (async (index) => {
        await func().then(value => {
          temp[index] = value;
          console.log(`❓ index =`, index);
          console.log(`value =`, value);
          console.log(`temp =`, temp);
          if(temp.length === functions.length) {
            return resolve(temp);
          }
          // temp = (3) [4, empty, 16] ❌
          // if(temp.length === functions.length && !temp.some(v => Object.prototype.toString.call(v) === '[object Promise]')) {
          //   return resolve(temp);
          // }
        }).catch(err => {
          return reject(err);
        });
      })(i);
    }
  });
};


function promiseAll<T>(functions: Fn<T>[]): Promise<T[]> {
  return new Promise((resolve, reject) => {
    let temp = [];
    let index = 0;
    for(let [i, func] of Object.entries(functions)) {
      console.log(`✅ i =`, i);
      // console.log(`func =`, func);
      func().then(value => {
        // temp[i] = value;
        temp[index] = value;
        index += 1;
        // temp.push(value);
        console.log(`❓ i =`, i);
        // index 0 twice bug ❌ 覆盖 bug
        // 💩 temp = [ 4, <1 empty item>, 16 ]
        console.log(`value =`, value);
        console.log(`temp =`, temp);
        // value = 16
        // temp = [ 4, <1 empty item>, 16 ] 2
        // setTimeout 时间先后顺序 bug ❌
        if(temp.length === functions.length && !temp.some(v => Object.prototype.toString.call(v) === '[object Promise]')) {
          return resolve(temp);
        }
        // setTimeout 时间先后顺序 bug ❌
        // setTimeout(() => {
        //   if(temp.length === functions.length) {
        //     return resolve(temp);
        //   }
        // }, 0);
      }).then(() => {
        // setTimeout 时间先后顺序 bug ❌
        // console.log(`temp =`, temp);
        // if(temp.length === functions.length) {
        //   return resolve(temp);
        // }
      }).catch(err => {
        return reject(err);
      }).finally(() => {
        // setTimeout 时间先后顺序 bug ❌
        // console.log(`temp =`, temp);
        // if(temp.length === functions.length) {
        //   return resolve(temp);
        // }
      });
      // if(temp.length === functions.length) {
      //   return resolve(temp);
      // }
      // let id = setInterval(() => {
      //   if(temp.length === functions.length && !temp.some(v => Object.prototype.toString.call(v) === '[object Promise]')) {
      //     clearInterval(id);
      //     return resolve(temp);
      //   }
      // }, 0);
    }
  });
};

function promiseAll() {
  return new Promise((resolve, reject) => {
    let temp = [];
    for(let [i, func] of Object.entries(functions)) {
      // console.log(`i =`, i);
      // console.log(`func =`, func);
      func().then(value => {
        console.log(`value =`, value);
        temp[i] = value;
        console.log(`temp =`, temp, i);
      }).catch(err => {
        return reject(err);
      });
    }
    // ❌ bug
    console.log(`temp ? =`, temp);
    setTimeout(() => {
      console.log(`temp =`, temp);
      if(temp.length === functions.length) {
        return resolve(temp);
      }
    }, 0);
  });
};

问题剖析

type Fn<T> = () => Promise<T>

function promiseAll<T>(functions: Fn<T>[]): Promise<T[]> {
  return new Promise((resolve, reject) => {
    let temp = [];
    let count = 0;
    for(let [i, func] of Object.entries(functions)) {
      func().then(value => {
        temp[i] = value;
        count += 1;
        // count ✅
        // if(count === functions.length) {
        //   return resolve(temp);
        // }
        // bug ❌
        // 使用 temp[i] = promise 赋值的时候 temp 长度就具有了；
        // 但是此时 promise 可能还没有返回结果，从而导致出现 empty 值的bug 
        // temp = (3) [4, empty, 16] ❌
        // i = 2 时候，temp 长度为 3， 但是此时 temp[1] 的 setTimeout 还没有返回结果，故出现 empty bug ❌
        if(temp.length === functions.length) {
          return resolve(temp);
        }
      }).catch(err => reject(err));
    }
  });
};

solutions

type Fn<T> = () => Promise<T>

function promiseAll<T>(functions: Fn<T>[]): Promise<T[]> {
  return new Promise((resolve, reject) => {
    let temp = [];
    let count = 0;
    for(let [i, func] of Object.entries(functions)) {
      func().then(value => {
        temp[i] = value;
        count += 1;
        // count ✅
        // 使用 count 避免出现 empty 返回值情况 ✅
        if(count === functions.length) {
          return resolve(temp);
        }
      }).catch(err => reject(err));
    }
  });
};

demos

LeetCode 2721. Execute Asynchronous Functions in Parallel

function promiseAll() {
  return new Promise((resolve, reject) => {
    let temp = [];
    let count = 0;
    for(let [i, func] of Object.entries(functions)) {
      func().then(value => {
        temp[i] = value;
        count += 1;
        // count ✅
        // 使用 count 避免出现 empty 返回值情况 ✅
        if(count === functions.length) {
          return resolve(temp);
        }
      }).catch(err => reject(err));
    }
  });
};

const functions = [() => new Promise(resolve => setTimeout(() => resolve(4), 50)), () => new Promise(resolve => setTimeout(() => resolve(10), 150)), () => new Promise(resolve => setTimeout(() => resolve(16), 100))];

promiseAll(functions).then(console.log);

https://leetcode.com/problems/execute-asynchronous-functions-in-parallel/description/?envType=study-plan-v2&envId=30-days-of-javascript

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refs

https://leetcode.com/problems/execute-asynchronous-functions-in-parallel/solutions/5194050/leetcode-promiseall/

https://leetcode.com/problems/execute-asynchronous-functions-in-parallel/solutions/3888598/promises-are-confusing-i-wrote-some-notes-down-for-you/

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