我有如下的示例代码，但是resolve后得到是空，因为在for中使用了多个异步获取的函数，导致了最终获得的结果只有1条，各位大神出来帮忙给点意见，主要目的是学习Promise
var arr1= [
{id:1,name:'Jason', age: 23, content:'我是来学习的家伙'},
{id:2,name:'Jason2', age: 23, content:'我是来学习的家伙'},
{id:3,name:'Jason3', age: 23, content:'我是来学习的家伙'},
{id:4,name:'Jason4', age: 23, content:'我是来学习的家伙'},
{id:5,name:'Jason5', age: 23, content:'我是来学习的家伙'},
{id:6,name:'Jason6', age: 23, content:'我是来学习的家伙'},
{id:7,name:'Jason7', age: 23, content:'我是来学习的家伙'},
{id:8,name:'Jason8', age: 23, content:'我是来学习的家伙'},
{id:9,name:'Jason9', age: 23, content:'我是来学习的家伙'},
{id:10,name:'Jason11', age: 23, content:'我是来学习的家伙'},
{id:11,name:'Jason12', age: 23, content:'我是来学习的家伙'},
{id:12,name:'Jason13', age: 23, content:'我是来学习的家伙'},
{id:13,name:'Jason14', age: 23, content:'我是来学习的家伙'},
{id:14,name:'Jason15', age: 23, content:'我是来学习的家伙'},
{id:15,name:'Jason16', age: 23, content:'我是来学习的家伙'},
{id:16,name:'Jason17', age: 23, content:'我是来学习的家伙'},
{id:17,name:'Jason18', age: 23, content:'我是来学习的家伙'},
{id:18,name:'Jason19', age: 23, content:'我是来学习的家伙'},
{id:19,name:'Jason22', age: 23, content:'我是来学习的家伙'},
{id:20,name:'Jason23', age: 23, content:'我是来学习的家伙'},
{id:21,name:'Jason24', age: 23, content:'我是来学习的家伙'},
{id:22,name:'Jason25', age: 23, content:'我是来学习的家伙'},
{id:23,name:'Jason26', age: 23, content:'我是来学习的家伙'},
{id:24,name:'Jason27', age: 23, content:'我是来学习的家伙'},
{id:25,name:'Jason28', age: 23, content:'我是来学习的家伙'},
{id:26,name:'Jason29', age: 23, content:'我是来学习的家伙'},
{id:27,name:'Jason33', age: 23, content:'我是来学习的家伙'},
{id:28,name:'Jason34', age: 23, content:'我是来学习的家伙'},
{id:29,name:'Jason35', age: 23, content:'我是来学习的家伙'},
{id:30,name:'Jason36', age: 23, content:'我是来学习的家伙'},
{id:31,name:'Jason37', age: 23, content:'我是来学习的家伙'},
{id:32,name:'Jason38', age: 23, content:'我是来学习的家伙'},
{id:34,name:'Jason39', age: 23, content:'我是来学习的家伙'},
{id:35,name:'Jason44', age: 23, content:'我是来学习的家伙'},
{id:36,name:'Jason41', age: 23, content:'我是来学习的家伙'},
{id:37,name:'Jason42', age: 23, content:'我是来学习的家伙'},
{id:38,name:'Jason43', age: 23, content:'我是来学习的家伙'}
]
var arr2 = [
{class:'一年级2班', userId: 33},
{class:'一年级3班', userId: 3},
{class:'一年级2班', userId: 5},
{class:'一年级6班', userId: 38},
{class:'一年级2班', userId: 21},
{class:'一年级3班', userId: 2},
{class:'一年级2班', userId: 1},
{class:'一年级9班', userId: 5},
{class:'一年级2班', userId: 7},
{class:'一年级1班', userId: 10},
{class:'一年级2班', userId: 13},
{class:'一年级5班', userId: 23}
]
var arr3 = [
{scope:80, userId: 21},
{scope:50, userId: 5},
{scope:70, userId: 10},
{scope:20, userId: 23},
{scope:70, userId: 13},
{scope:44, userId: 3},
{scope:23, userId: 33},
{scope:76, userId: 1},
{scope:45, userId: 10},
{scope:26, userId: 38},
{scope:65, userId: 7},
{scope:45, userId: 30},
{scope:76, userId: 22},
{scope:46, userId: 4},
{scope:95, userId: 8},
{scope:100, userId: 9},
{scope:74, userId: 35}
]
//获取所以学生的名字和ID
function getName() {
return new Promise((resolve, reject) => {
let cf = []
arr1.map(item => {
cf.push({id: item.id,name:item.name})
})
resolve(cf)
})
}
//获取学生的分数
function getScope(id) {
return new Promise((resolve,reject) => {
arr3.map(item=>{
if(id == item.userId){
resolve(item.scope)
}
})
})
}
function allPromise() {
return new Promise((resolve, reject) => {
let data = []
getName().then(res => {
console.log('res', res)
let promise1 = []
for (var i = 0; i < res.length; i++) {
let name = res[i].name
let id = res[i].id
let classes, scope
for (var j = 0; j < arr2.length; j++) {
if (arr2[j].userId == id) {
classes = arr2[j].class
getScope(id).then(result => {
scope = result
data.push({
id: id,
name: name,
class: classes,
scope: scope
})
})
}
}
}
})
console.log(data)
resolve(data)
})
}
在for循环中，我们通常会使用同步获取的方式来获取数据，例如使用fetch()方法或XMLHttpRequest对象。然而，如果我们想要获取异步数据，我们可以使用回调函数、Promise或者async/await等方法。
以下是一个使用Promise的例子：
javascript
for (let i = 0; i < 10; i++) {
setTimeout(() => {
const data = await fetch('https://api.example.com/data');
console.log(data);
}, i * 1000);
}
在这个例子中，fetch()方法返回一个Promise，然后我们使用then()方法处理这个Promise。then()方法接受一个回调函数，这个回调函数会在Promise被解决或者被拒绝时被调用。
如果你使用的是async/await，那么你可以这样做：
```javascript async function fetchData() { for (let i = 0; i < 10; i++) { const data = await fetch('https://api.example.com/data'); console.log(data); } }
fetchData(); ```
在这个例子中，fetchData()函数是一个async函数，它会立即开始执行。然后，我们使用await关键字等待fetchData()函数完成。一旦fetchData()函数完成，我们就调用console.log()来打印获取的数据。
无论你使用哪种方法，都可以保证异步获取的数据不会阻塞整个for循环的执行。
