解决await在forEach中不起作用的问题

const _ = require('lodash');
const echo = async (i) => {
  setTimeout(() => {
    console.log('i===>', i);
  }, 5000);
}
let arrs = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const task = async () => {
  _.forEach(arrs, async (i) => {
    await echo(i);
  })
}
const run = async () => {
  console.log('run-start====>date:', new Date().toLocaleDateString())
  await task() ;
  console.log('run-end====>date:', new Date().toLocaleDateString())
}
(async () => {
  console.log('start...')
  await run();
  console.log('end...')
})()
// start...
// run-start====>date: 2018-8-25
// run-end====>date: 2018-8-25
// end...
// i===> 1
// i===> 2
// i===> 3
// i===> 4
// i===> 5
// i===> 6
// i===> 7
// i===> 8
// i===> 9

const _ = require('lodash');
const echo = async (i) => {
  return new Promise((resolve,reject)=>{
    setTimeout(() => {
      console.log('i===>', i,new Date().toLocaleTimeString());
      resolve(i) ;
    }, 2000);
  })
}
let arrs = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const task = async () => {
  // _.forEach(arrs, async (i) => {
  //  await echo(ji) ;
  // })
  // arrs.forEach(async (i )=> {
  //   await echo(i) ;
  // });
  for (const i of arrs) {
    await echo(i) ;
  }
}
const run = async () => {
  console.log('run-start====>date:', new Date().toLocaleDateString())
  await task() ;
  console.log('run-end====>date:', new Date().toLocaleDateString())
}
(async () => {
  console.log('start...')
  await run();
  console.log('end...')
})()
// 输出
start...
run-start====>date: 2018-8-26
i===> 1 20:51:29
i===> 2 20:51:31
i===> 3 20:51:33
i===> 4 20:51:35
i===> 5 20:51:37
i===> 6 20:51:39
i===> 7 20:51:42
i===> 8 20:51:44
i===> 9 20:51:46
i===> 10 20:51:48
run-end====>date: 2018-8-26
end...

// 生成数据
const getNumbers = () => {
 return Promise.resolve([1, 2, 3])
}
// 异步处理
const doMulti = num => {
 return new Promise((resolve, reject) => {
  setTimeout(() => {
   if (num) {
    resolve(num * num)
   } else {
    reject(new Error('num not specified'))
   }
  }, 2000)
 })
}
// 主函数
const main = async () => {
 console.log('start');
 const nums = [1, 2, 3];
 nums.forEach(async (x) => {
  const res = await doMulti(x);
  console.log(res);
 });
 console.log('end');
};
// 执行
main();

const main = async () => {
 console.log('start');
 const nums = await getNumbers();
 for (const x of nums) {
  const res = await doMulti(x);
  console.log(res);
 }
 console.log('end');
};

// Production steps of ECMA-262, Edition 5, 15.4.4.18
// Reference: http://es5.github.io/#x15.4.4.18
if (!Array.prototype.forEach) {
 Array.prototype.forEach = function(callback, thisArg) {
  var T, k;
  if (this == null) {
   throw new TypeError(' this is null or not defined');
  }
  // 1. Let O be the result of calling toObject() passing the
  // |this| value as the argument.
  var O = Object(this);
  // 2. Let lenValue be the result of calling the Get() internal
  // method of O with the argument "length".
  // 3. Let len be toUint32(lenValue).
  var len = O.length >>> 0;
  // 4. If isCallable(callback) is false, throw a TypeError exception. 
  // See: http://es5.github.com/#x9.11
  if (typeof callback !== "function") {
   throw new TypeError(callback + ' is not a function');
  }
  // 5. If thisArg was supplied, let T be thisArg; else let
  // T be undefined.
  if (arguments.length > 1) {
   T = thisArg;
  }
  // 6. Let k be 0
  k = 0;
  // 7. Repeat, while k < len
  while (k < len) {
   var kValue;
   // a. Let Pk be ToString(k).
   //  This is implicit for LHS operands of the in operator
   // b. Let kPresent be the result of calling the HasProperty
   //  internal method of O with argument Pk.
   //  This step can be combined with c
   // c. If kPresent is true, then
   if (k in O) {
    // i. Let kValue be the result of calling the Get internal
    // method of O with argument Pk.
    kValue = O[k];
    // ii. Call the Call internal method of callback with T as
    // the this value and argument list containing kValue, k, and O.
    callback.call(T, kValue, k, O);
   }
   // d. Increase k by 1.
   k++;
  }
  // 8. return undefined
 };
}

Array.prototype.forEach = function (callback) {
 // this represents our array
 for (let index = 0; index < this.length; index++) {
  // We call the callback for each entry
  callback(this[index], index, this);
 };
};

const main = async () => {
 console.log('start');
 const nums = await getNumbers();
 // nums.forEach(async (x) => {
 //  const res = await doMulti(x);
 //  console.log(res);
 // });
 for (let index = 0; index < nums.length; index++) {
  (async x => {
   const res = await doMulti(x)
   console.log(res)
  })(nums[index])
 }
 console.log('end');
};

const asyncForEach = async (array, callback) => {
 for (let index = 0; index < array.length; index++) {
  await callback(array[index], index, array);
 }
}
const main = async () => {
 console.log('start');
 const nums = await getNumbers();
 await asyncForEach(nums, async x => {
  const res = await doMulti(x)
  console.log(res)
 })
 console.log('end');
};
main();

async function foo(things) {
 const results = [];
 for (const thing of things) {
  // Good: all asynchronous operations are immediately started.
  results.push(bar(thing));
 }
 // Now that all the asynchronous operations are running, here we wait until they all complete.
 return baz(await Promise.all(results));
}

async function foo(things) {
 const results = [];
 for (const thing of things) {
  // Bad: each loop iteration is delayed until the entire asynchronous operation completes
  results.push(await bar(thing));
 }
 return baz(results);
}