[英]How to call a JavaScript function sequentially in a for loop?
I want to pass each item into a function that take times.我想将每个项目传递给一个需要时间的函数。 But seems that the JS function is asynchronized.
但似乎JS功能是异步的。 How can I call the function sequentially ?
如何按顺序调用该函数? (Pass next item to function after the previous done)
(在上一个完成后将下一个项目传递给函数)
function main() {
for (var i = 0; i < n ; i++) {
doSomething(myArray[i]);
}
}
function doSomething(item) {
// do something take time
}
My solution is call the function recusively.我的解决方案是递归调用该函数。 But I want to know is there a different way to solve this issue ?
但我想知道有没有不同的方法来解决这个问题? Thanks.
谢谢。
function main() {
doSomething(myArray, 0);
}
function doSomething(item, i) {
// do something take time
doSomething(myArray, i + 1);
}
In JavaScript, as of 2020, the for-loop is async/await aware.在 JavaScript 中,截至 2020 年,for 循环具有异步/等待感知能力。 You can return a promise and then
await
that promise inside of the for loop.您可以返回一个承诺,然后在 for 循环内
await
该承诺。 This causes the loop to execute in a series, even for long running operations.这会导致循环连续执行,即使是长时间运行的操作。
function randomSleep(ms, seed=10) {
ms = ms * Math.random() * seed;
return new Promise((resolve, reject)=>setTimeout(resolve, ms));
}
async function doSomething(idx) {
// long running operations
const outcome = await randomSleep(500);
return idx;
}
const arrItems = ['a','b','c','d'];
for(let i=0,len=arrItems.length;i<len;i++) {
const result = await doSomething(i);
console.log("result is", result)
}
Read more about async await in for loops and forEach loops here https://zellwk.com/blog/async-await-in-loops/在此处阅读有关 for 循环和 forEach 循环中的异步等待的更多信息https://zellwk.com/blog/async-await-in-loops/
if you want to pass next item to function after the previous done, you can try to use promise, just like this如果你想在上一个完成后将下一个项目传递给函数,你可以尝试使用promise,就像这样
var Q = require('q');
var promise;
main();
function main() {
promise = doSomethingPromise(0)
for (var i = 1; i < 10 ; i++) {
(function (i) {
promise = promise.then(function (res) {
return doSomethingPromise(res + ' ' + i)
});
})(i)
}
}
function doSomethingPromise (item) {
var d = Q.defer();
d.resolve(doSomething(item));
return d.promise;
}
function doSomething(item) {
// do something take time
console.log('doSomething', item);
return item;
}
it can make you function to be called by order.它可以让您按顺序调用函数。
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