在一系列异步调用之后使用Future返回

Question

I am writing a JavaScript (node.js) function that makes several exec() calls (asynchronously) and I need to use Future to return after all of them are completed.

What I have is:

run: function(command, callback) {
  for (var i = 0; i < testCases.length; i++) {
    var child = exec(command, options, function(error, stdout, stderr) {
      // calculate `answer`

      if (answer == "wrong") callback(answer);
    });
  }
},

So, if answer is "wrong", then I can easily call the callback and that's it. However, if all the answers aren't "wrong" (in other words, if all the exec have answer=="correct" ) then I have no idea of how to return such value.

I know I can use Future (from npm ) for this. However, I can't really see how to use it in this case (where I don't have just 1 async call, but multiple async calls).

Answer 1

Try async library

async.times(testCases.length, function(n, next){
    var child = exec(command, options, function(error, stdout, stderr) {
      // calculate `answer`

      var data = {answer : answer};
      if (answer == "wrong") {
        next({err: answer}, data);
      }
      else {
        next(null, data);
      }
    });
}, callback(err, data) {
    // you can also check for err
  // we now have an array of data[testCases.length]
});

Answer 2

One way to do it would be to check for the number of commands completed -

var totalCompleted = 0;
var done = false;
for (var i = 0; i < testCases.length; i++) {
    var child = exec(command, options, function(error, stdout, stderr) {
      // calculate `answer`
      totalCompleted++;
      if (answer == "wrong" && !done) {
         done = true;
         return callback(answer);
      }
      if(totalCompleted === testCases.length && !done) {
         callback('right');
      }

    });
  }