I read through various threads like this one for example.
But it really escapes me how to accomplish the following:
I have 4 functions, and want them happen one after another in sequence. Notice they are in incorrect order, to get my point across. I want the result that will output "1, 2, 3, 4'
function firstFunction(){
// some very time consuming asynchronous code...
console.log('1');
}
function thirdFunction(){
// definitely dont wanna do this until secondFunction is finished
console.log('3');
}
function secondFunction(){
// waits for firstFunction to be completed
console.log('2');
}
function fourthFunction(){
// last function, not executed until the other 3 are done.
console.log('4');
}
I tried to figure out callbacks but am getting lost :(
Isn't there some simple way to do this? Like looping through an array...
It's a great chance to start using jQuery Deferred.
Apart from the callbacks-based solution the code is readable, flexible and highly maintainable
http://jsfiddle.net/zerkms/zJhph/
function firstFunction(){
var d = $.Deferred();
// some very time consuming asynchronous code...
setTimeout(function() {
console.log('1');
d.resolve();
}, 1000);
return d.promise();
}
function thirdFunction(){
var d = $.Deferred();
// definitely dont wanna do this until secondFunction is finished
setTimeout(function() {
console.log('3');
d.resolve();
}, 1000);
return d.promise();
}
function secondFunction(){
var d = $.Deferred();
setTimeout(function() {
console.log('2');
d.resolve();
}, 1000);
return d.promise();
}
function fourthFunction(){
var d = $.Deferred();
// last function, not executed until the other 3 are done.
setTimeout(function() {
console.log('4');
d.resolve();
}, 1000);
return d.promise();
}
firstFunction().pipe(secondFunction).pipe(thirdFunction).pipe(fourthFunction);
PS: as an example of asynchronous code I've used setTimeout
. The main thing is that in the end of the asynchronous part you need to call d.resolve()
to continue chaining methods.
Further reading: http://joseoncode.com/2011/09/26/a-walkthrough-jquery-deferred-and-promise/