正如标题所示。我怎么做呢?
我想在foreach循环遍历每个元素并完成一些异步处理后调用whenAllDone()。
[1, 2, 3].forEach(
function(item, index, array, done) {
asyncFunction(item, function itemDone() {
console.log(item + " done");
done();
});
}, function allDone() {
console.log("All done");
whenAllDone();
}
);
有可能让它这样工作吗?当forEach的第二个参数是一个回调函数，当它经过所有迭代时运行?
预期的输出:
3 done
1 done
2 done
All done!
当前回答
我没有承诺的解决方案(这可以确保每个动作在下一个动作开始之前结束):
Array.prototype.forEachAsync = function (callback, end) { var self = this; function task(index) { var x = self[index]; if (index >= self.length) { end() } else { callback(self[index], index, self, function () { task(index + 1); }); } } task(0); }; var i = 0; var myArray = Array.apply(null, Array(10)).map(function(item) { return i++; }); console.log(JSON.stringify(myArray)); myArray.forEachAsync(function(item, index, arr, next){ setTimeout(function(){ $(".toto").append("<div>item index " + item + " done</div>"); console.log("action " + item + " done"); next(); }, 300); }, function(){ $(".toto").append("<div>ALL ACTIONS ARE DONE</div>"); console.log("ALL ACTIONS ARE DONE"); }); <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div class="toto"> </div>
其他回答
如果使用setInterval来检查完整的迭代计数，会带来保证。虽然不确定它是否不会超载范围，但我使用它，似乎是一个
_.forEach(actual_JSON, function (key, value) {
// run any action and push with each iteration
array.push(response.id)
});
setInterval(function(){
if(array.length > 300) {
callback()
}
}, 100);
我没有承诺的解决方案(这可以确保每个动作在下一个动作开始之前结束):
Array.prototype.forEachAsync = function (callback, end) { var self = this; function task(index) { var x = self[index]; if (index >= self.length) { end() } else { callback(self[index], index, self, function () { task(index + 1); }); } } task(0); }; var i = 0; var myArray = Array.apply(null, Array(10)).map(function(item) { return i++; }); console.log(JSON.stringify(myArray)); myArray.forEachAsync(function(item, index, arr, next){ setTimeout(function(){ $(".toto").append("<div>item index " + item + " done</div>"); console.log("action " + item + " done"); next(); }, 300); }, function(){ $(".toto").append("<div>ALL ACTIONS ARE DONE</div>"); console.log("ALL ACTIONS ARE DONE"); }); <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div class="toto"> </div>
在ES2018中，你可以使用异步迭代器:
const asyncFunction = a => fetch(a);
const itemDone = a => console.log(a);
async function example() {
const arrayOfFetchPromises = [1, 2, 3].map(asyncFunction);
for await (const item of arrayOfFetchPromises) {
itemDone(item);
}
console.log('All done');
}
希望这将解决你的问题，我通常与此工作时，我需要执行forEach与异步任务。
foo = [a,b,c,d];
waiting = foo.length;
foo.forEach(function(entry){
doAsynchronousFunction(entry,finish) //call finish after each entry
}
function finish(){
waiting--;
if (waiting==0) {
//do your Job intended to be done after forEach is completed
}
}
与
function doAsynchronousFunction(entry,callback){
//asynchronousjob with entry
callback();
}
在这个帖子中有许多解决方案和方法来实现这一点!
但是，如果你需要用map和async/await来做这个，那么这里就是
// Execution Starts
console.log("start")
// The Map will return promises
// the Execution will not go forward until all the promises are resolved.
await Promise.all(
[1, 2, 3].map( async (item) => {
await asyncFunction(item)
})
)
// Will only run after all the items have resolved the asynchronous function.
console.log("End")
输出将如下所示!可能根据异步函数而有所不同。
start
2
3
1
end
注意:如果你在map中使用await，它总是会返回promises数组。
