What is the best way to ensure that a specific number of XHR callbacks have successfully completed before proceeding with further actions?

Question

What is the best way to ensure that a specific number of XHR callbacks have successfully completed before proceeding with further actions?

I have four requests that each have their own callback and can fire in any order. However, I need all the callbacks to finish successfully before executing mergeData.

The issue with my current approach is that the initial parameter values do not refresh once waitForSync is called (and I am not confident in this method). Can anyone guide me in the right direction?

var heroes = requestDataFromAPI('heroes');
var weapons = requestDataFromAPI('weapons');
var races = requestDataFromAPI('races');
var jobs = requestDataFromAPI('jobs');

waitForSync(heroes, weapons, races, jobs);

...

function waitForSync(heroes, weapons, races, jobs){
  if (heroes && weapons && races && jobs) {
    mergeData(heroes, weapons, races, jobs);
  }
  else {
    setTimeout(waitForSync, '500', heroes, weapons, races, jobs);
  }
}

javascript ajax callback

Answer 1

Answer №1

What types are they? Are they regular XHR objects or jQuery XHRs? Regardless, both will return true when converted to booleans, making the condition also evaluate to true.

You could modify your code to monitor readystate and increase a counter, but I personally prefer using Q promises for a different approach.

This method also allows for easy error handling,

For instance (assuming that requestDataFromAPI returns a jQuery XHR):

// Convert jQuery XHRs into Q promises

var heroesPromise = Q(requestDataFromAPI('heroes'));
var weaponsPromise = Q(requestDataFromAPI('weapons'));
var racesPromise = Q(requestDataFromAPI('races'));
var jobsPromise = Q(requestDataFromAPI('jobs'));

// Wait for all promises to complete

Q.all([heroesPromise, weaponsPromise, racesPromise, jobsPromise])
  .spread(function (heroes, weapons, races, jobs) {
    // Process results
    console.log(heroes, weapons, races, jobs);    
  })
  .catch(function (err) {
    console.log('An error occurred', err);
  })
  .done();

If you're new to promises, I recommend taking the time to learn about them. They simplify handling asynchronous operations and help avoid unnecessary complexities. You won't regret it.

The provided article discusses native promises, but until they are universally supported by browsers, using libraries like Q is necessary. It's also important to note: avoid using jQuery promises as they have limitations (which is why I use Q() wrappers).

Answer 2

What types are they? Are they regular XHR objects or jQuery XHRs? Regardless, both will return true when converted to booleans, making the condition also evaluate to true.

You could modify your code to monitor readystate and increase a counter, but I personally prefer using Q promises for a different approach.

This method also allows for easy error handling,

For instance (assuming that requestDataFromAPI returns a jQuery XHR):

// Convert jQuery XHRs into Q promises

var heroesPromise = Q(requestDataFromAPI('heroes'));
var weaponsPromise = Q(requestDataFromAPI('weapons'));
var racesPromise = Q(requestDataFromAPI('races'));
var jobsPromise = Q(requestDataFromAPI('jobs'));

// Wait for all promises to complete

Q.all([heroesPromise, weaponsPromise, racesPromise, jobsPromise])
  .spread(function (heroes, weapons, races, jobs) {
    // Process results
    console.log(heroes, weapons, races, jobs);    
  })
  .catch(function (err) {
    console.log('An error occurred', err);
  })
  .done();

If you're new to promises, I recommend taking the time to learn about them. They simplify handling asynchronous operations and help avoid unnecessary complexities. You won't regret it.

The provided article discusses native promises, but until they are universally supported by browsers, using libraries like Q is necessary. It's also important to note: avoid using jQuery promises as they have limitations (which is why I use Q() wrappers).

Answer 3

Answer №2

To enhance your requestDataFromAPI(String) method, you can modify it as requestDataFromAPI(String, Function), with the callback function as the second parameter.

After completing the requestDataFromAPI call, execute the callback function.

requestDataFromAPI = function(type, callback) {
    ....
    callback();
}

Redefine your entire script in the following manner:

var heroes = false,
weapons = false,
races = false,
jobs = false,
waitForSync= function(){
  if (heroes && weapons && races && jobs) {
    mergeData(heroes, weapons, races, jobs);
  }
};

requestDataFromAPI('heroes', function(){heroes = true; waitForSync();});
requestDataFromAPI('weapons', function(){weapons = true; waitForSync();});
requestDataFromAPI('races', function(){races = true; waitForSync();});
requestDataFromAPI('jobs', function(){jobs = true; waitForSync();});

Answer 4

To enhance your requestDataFromAPI(String) method, you can modify it as requestDataFromAPI(String, Function), with the callback function as the second parameter.

After completing the requestDataFromAPI call, execute the callback function.

requestDataFromAPI = function(type, callback) {
    ....
    callback();
}

Redefine your entire script in the following manner:

var heroes = false,
weapons = false,
races = false,
jobs = false,
waitForSync= function(){
  if (heroes && weapons && races && jobs) {
    mergeData(heroes, weapons, races, jobs);
  }
};

requestDataFromAPI('heroes', function(){heroes = true; waitForSync();});
requestDataFromAPI('weapons', function(){weapons = true; waitForSync();});
requestDataFromAPI('races', function(){races = true; waitForSync();});
requestDataFromAPI('jobs', function(){jobs = true; waitForSync();});

What is the best way to ensure that a specific number of XHR callbacks have successfully completed before proceeding with further actions?

Answer №1

Answer №2

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