I'm using a for each to process a list and i want that element n to be executed only when element n-1 is over:
var elements = ["stuff1", "stuff2", "stuff3"];
elements.forEach(function(element){
someAsyncFunction(element, function(){
console.log('do more stuff');
});
});
I need that they wait for each other and execute in the right order.
EDIT : I bumped into process.nextTick(), but I'm not sure if it guarantees the waiting and order.
Just store the elements in an array exactly the same way as you did in your question. Then use elements.shift() to retrieve and remove the first element.
var elements = ["stuff1", "stuff2", "stuff3"];
(function next () {
if (!elements.length) {
return;
}
var element = elements.shift();
someAsyncFunction(element, function (err, result) {
…
next();
});
})();
A nice way is to make use of a promise library like Q or Bluebird and then implement a promiseWhile like this.
var Promise = require('bluebird');
var promiseWhile = function(condition, action) {
var resolver = Promise.defer();
var loop = function() {
if (!condition()) return resolver.resolve();
return Promise.cast(action())
.then(loop)
.catch(resolver.reject);
};
process.nextTick(loop);
return resolver.promise;
};
Usage:
var sum = 0,
stop = 10;
promiseWhile(function() {
// Condition for stopping
return sum < stop;
}, function() {
// Action to run, should return a promise
return new Promise(function(resolve, reject) {
// Arbitrary 250ms async method to simulate async process
// In real usage it could just be a normal async event that
// returns a Promise.
setTimeout(function() {
sum++;
// Print out the sum thus far to show progress
console.log(sum);
resolve();
}, 250);
});
}).then(function() {
// Notice we can chain it because it's a Promise,
// this will run after completion of the promiseWhile Promise!
console.log("Done");
});