2705. JavaScript - Async Call in Loop[Draft]Async
Introduce how to implement Async call in loop, like array.
23. Async in loop
async for loop in node.js https://stackoverflow.com/questions/21184340/async-for-loop-in-node-js
Execute in parallel.
var results = [];
var config = JSON.parse(queries);
var onComplete = function() {
res.writeHead( ... );
res.end(results);
};
var keys = Object.keys(config);
var tasksToGo = keys.length;
if (tasksToGo === 0) {
onComplete();
} else {
// There is at least one element, so the callback will be called.
keys.forEach(function(key) {
var query = config[key].query;
search(query, function(result) {
results.push(result);
if (--tasksToGo === 0) {
// No tasks left, good to go
onComplete();
}
});
});
}
If the functions need to be called in a specific order, then you can use recursion to get the desired effect:
var results = [];
var config = JSON.parse(queries);
var keys = Object.keys(config);
(function next(index) {
if (index === keys.length) { // No items left
res.writeHead( ... );
res.end(results);
return;
}
var key = keys[index];
var query = config[key].query;
search(query, function(result) {
results.push(result);
next(index + 1);
});
})(0);
To simplify the above code, use async
.
https://github.com/caolan/async
var async = require("async");
var obj = {dev: "/dev.json", test: "/test.json", prod: "/prod.json"};
var configs = {};
async.forEachOf(obj, (value, key, callback) => {
fs.readFile(__dirname + value, "utf8", (err, data) => {
if (err) return callback(err);
try {
configs[key] = JSON.parse(data);
} catch (e) {
return callback(e);
}
callback();
});
}, err => {
if (err) console.error(err.message);
// configs is now a map of JSON data
doSomethingWith(configs);
});