這裏是實現一個循環來進行計算(模擬異步數據庫調用)的一種非常原始的方式通過使用事件。由於Brmm暗示,一旦你走異步,你必須一路走向異步。下面的代碼只是一個示例,讓您瞭解理論上的過程應該是什麼樣子。有幾個庫可以處理異步呼叫的同步過程,並且您還希望查看以下內容:
var events = require('events');
var eventEmitter = new events.EventEmitter();
var total = 0;
var count = 0;
var keys = [];
// Loop through the items
calculatePrice = function(keys) {
for (var i = 0; i < keys.length; i++) {
key = keys[i];
eventEmitter.emit('getPriceFromDb', {key: key, count: keys.length});
};
}
// Get the price for a single item (from a DB or whatever)
getPriceFromDb = function(data) {
console.log('fetching price for item: ' + data.key);
// mimic an async db call
setTimeout(function() {
price = data.key * 10;
eventEmitter.emit('aggregatePrice', {key: data.key, price: price, count: data.count});
}, 500);
}
// Agregate the price and figures out if we are done
aggregatePrice = function(data) {
count++;
total += data.price;
console.log('price $' + price + ' total so far $' + total);
var areWeDone = (count == data.count);
if (areWeDone) {
eventEmitter.emit('done', {key: data.key, total: total});
}
}
// We are done.
displayTotal = function(data) {
console.log('total $ ' + data.total);
}
// Wire up the events
eventEmitter.on('getPriceFromDb', getPriceFromDb);
eventEmitter.on('aggregatePrice', aggregatePrice);
eventEmitter.on('done', displayTotal);
// Kick of the calculate process over an array of keys
keys = [1, 2, 3]
calculatePrice(keys);