Javascript承诺混乱以按顺序执行两个功能

Question

Right now I have funcA, funcB, arrayA and arrayB. In funcA, arrayB will populate itself by requesting some external information and the time for doing this is varied. I want it to execute funcB after arrayB.length == arrayA.length, and arrayB is a global variable that its content will be used in funcB. I assume that I need to use JQuery deferred and promise..so I tried this

     var arrayB = [];
     var hi = funcA();
     hi.then(funcB());

     funcA(){
            var Dfd = $.Deferred();
            arrayB.forEach(function(x, i){
                   some external retrieval;
                   if (arrayB.length == arrayA.length){
                         Dfd.resolve(arrayB);
                   }
             })

        return Dfd;
     }

But this doesn't help. How should I change it?

Answer 1

arrayB.forEach won't do a thing. It's empty. Forget all this functions and deferred.

fetch('/mydata.json')
  .then(function(response) {
    //save your data from response to arrayB
    //call your funcA
  })
  .catch((error) => {
    console.log(error);
});

I don't know why you needed that:

if (arrayB.length == arrayA.length){
   Dfd.resolve(arrayB);
}

But feel free to make a check before calling funcA.

Answer 2

我这样做可以解决问题：

  hi.done(function(){funcA()});