Is prom.all useful given that javascript is executed in a single thread?

Question

In, for example, kriskowal Q, you can do something like:

promise1.then(function(p1){
  var p2 = makePromise2();
  var p3 = makePromise3();
  var p4 = makePromise4();
  return [p2, p3, p4];
})
.all(promises, function(){
  console.log('all promises fulfilled');
}, function(reason){
  console.log('a promise was rejected: ' + reason.toString());
});

Given that javascript is executed in a single thread, does this have any advantage, performance, or something else just by making a series of then () calls?

Answer 1

First of all, JavaScript as a language does not say anything about concurrency. In fact, in many scenarios you can create and run multi-threaded JavaScript-WebWorkers on the Internet, in node, and independently integrate the JS engine into an existing application.

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// with all
var a = ["url1","url2","url3"].map(makeAjaxPromise); // make 3 ajax calls
Promise.all(a).spread(function(res1,res2,res3){ // Q.all with Q
     alert("Everything loaded!");
});

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 makeAjaxPromise("url1").
 then(makeAjaxPromise.bind(null,"url2").
 then(makeAjaxPromise.bind(null,"url3").then(function(){
      alert("Everything loaded!"); // disregarding getting the data here
 });

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Answer 2

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