将promise与递归函数一起使用

Question

I am trying to figure out if it's possible to use promises instead of a standard callback in a recursive function.

The way I have it now:

function recursive(data, cb){

     (function promiseProvider(data){

          return newThenable(data).then(function(val){
                 if(val.a){
                    cb(null, val);
                 }
                 else {
                    return promiseProvider(val);
                 }

          });

     })(data);

}

This works, but I can't figure out how I could make a pure promise implementation.

Perhaps this would work?

  function recursive(data){

      return newThenable(data).then(function(val){
               if(val.a){
                  return // <<< ???
                 }
                 else {
                   return recursive(val);
                 }

        });

     }

However, that doesn't work.

Answer 1

Given you were calling the callback with val as the result argument, just

return val;

from the then callback. That's it.

function recursive(data){
     return newThenable(data).then(function(val){
         if (val.a){
             return val;
         } else {
             return recursive(val);
         }
     });
 }

Answer 2

Push val to an array. If val.a return array of results, else call recursive with val and array of accumulates results as parameter. See multiple, sequential fetch() Promise

  function recursive(data, results) {
    return newThenable(data).then(function(val) {
      if (val.a) {
        // results.push(val);
        return results
      } else {
        results.push(val);
        return recursive(val, results).catch(function(e) {console.log(e)});
      }
    });
  }

Answer 3

Nowadays the ES8 async/await makes it more readable. I skipped the try-catch for now.

async function recursive(data, results = []) {
    let val = await newThenable(data);
    if (val.a) {
        return results
    } else {
        results.push(val);
        return recursive(val, results);
    }
}