[英]How can I make a recursive Promise call to be the return for a reduce in Javascript?
我正在尝试在 JS 的reduce
中创建一个递归的Promise
调用。 我的系统的目标是对数组中的每个项目进行 n 个大调用, reduce
播放,然后,如果在该reduce
内部,该大调用决定它在返回大调用之前需要 n 个较小的调用,那么reduce
不应该跳到下一个项目,只需等待它完成即可。
我目前的代码是:
function download_preliminary_files_1() {
let demo_schema_download = new Base_Ajax_Requester(
localized_data.ajax_url,
{
'ajax_action': 'download_demo_file_schema',
'ajax_nonce': localized_data.ajax_nonce,
'backend': {
'data_handle': 'download_demo_file_schema_data',
'data':
{
'demo_handle' : 'demo-2',
}
}
}
);
let import_files_download = demo_schema_download.call().then(function() {
fake_data.steps_to_import.reduce(function(previous_promise, next_step_identifier) {
return previous_promise.then(function() {
let file_download = download_demo_file({
'demo_handle' : 'demo-2',
'step' : next_step_identifier
}).call();
file_download.then(function(response) {
/**
* Here, if I detect that response.remaining_number_of_files > 0, I should start
* a chain that keeps calling `download_demo_file` with new parameters.
*
* Then, when this chain is done, resume the normal reduce behavior.
*/
});
});
}, Promise.resolve())
}).catch(function(error) {
console.log( 'Got this error:' + error);
});
return import_files_download;
}
其中Base_Ajax_Requester
是一个辅助类,它处理 AJAX 请求并在完成时返回一个Promise
,以便可以围绕它编写代码。
我的fake_data
是:
let fake_data = {
'demo_handle' : 'demo-2',
'steps_to_import' : [ 'elementor-hf','post', 'nav_menu' ]
}
如您所见, fake_data.steps_to_import.reduce(..
将遍历这 3 个值,为每个值调用download_demo_file
,等待它完成,然后继续下一个。我们可以说我想,在elementor-hf
之间elementor-hf
并post
n 个较小的调用。
在那里可以看到对download_demo_file
的初始调用,这是从后端返回的内容:
{
'message' : '...',
'file_number' : 1, //Which -n.xml file has been downloaded where n is this number.
'remaining_number_of_files' : 1 //Calculates, based on what file was downloaded how many files are left. The system knows internally how many files it has to download.
}
再次调用download_demo_file
的重试调用将如下所示:
{
'demo_handle' : 'demo-2',
'step' : next_step_identifier,
'file_counter' : 2 //Dynamic. This will signal that it needs to now download file-2.xml.
}
...依此类推,直到后端发送remaining_number_of_files : 0
,然后一切都会停止,因为没有更多文件要下载,并且可以跳到下一个大调用。
我怎样才能做到这一点?
在每个reduce
回调中,我会创建一个调用download_demo_file
的函数(带有不断变化的file_counter
),在 Promise 解析之后,如果remaining_number_of_files > 0
file_counter
remaining_number_of_files > 0
则递归地返回自身调用。 这意味着getProm()
将不断调用自身,直到remaining_number_of_files > 0
getProm()
remaining_number_of_files > 0
条件不再满足,并且只有在此之后,该特定reduce
迭代的整个 Promise 才会解决。
let import_files_download = demo_schema_download.call().then(function() {
fake_data.steps_to_import.reduce(function(previous_promise, step) {
let file_counter = 1;
return previous_promise.then(function() {
const getProm = () => download_demo_file({
demo_handle: 'demo-2',
step,
file_counter
}).call()
.then((response) => {
file_counter++;
return response.remaining_number_of_files > 0
? getProm()
: response
});
return getProm();
});
}, Promise.resolve())
}).catch(function(error) {
console.log('Got this error:' + error);
});
该代码可能会是一个更容易阅读和理解与async
/ await
,虽然:
await demo_schema_download.call();
const import_files_download = [];
for (const step of fake_data.steps_to_import) {
let response;
let file_counter = 1;
do {
response = await download_demo_file({
demo_handle: 'demo-2',
step,
file_counter
}).call();
file_counter++;
} while (response.remaining_number_of_files > 0);
import_files_download.push(response); // is this needed?
}
return import_files_download; // is this needed?
捕获异步函数的使用者。
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