Question

In my former post I was able to solve my Promise problem by looking at some examples provided by this community. I hope this one will be easy to solve too, although I just can't get my head around it. For the first time in my life, I experience being fluent in PHP language is a burden.

My code looks like this:

let getProducts = function(){
  countProducts
    .then(function(number){
      var name = '';
      let list = [];
      getProductNames(name)
        .then(function(names){
          names.forEach(function(el){
            list.push(el);
          });
          name = list.pop();
          getProductNames(name)
            .then(function(names){
              names.forEach(function(el){
                list.push(el);
              });
              ... and some more code to put the names in a table

the getProductNames function looks like this:

var getProductNames = 
function(name) {
  return new Promise(
        function(resolve, reject){
            xyz.api.checkProducts(name, 1000, function(err, names){
              if (err){
                reject(err);
              } else {
                resolve(names);
              } 
            });
        }
  );
}

This works because I know I have less than 2000 products, each check returns 1000 products, so I have to run the getProductNames function twice.

What I am looking for is a way to make this into a loop so it automatically runs the needed number of runs.

The problem with the api call is that it needs a productname to start with. The first run is without a name, this returns the first 1000. For the second run I need the last found productname of run 1, for run 3 I need the last found productname of 2, and so on.

There are different ways to determine whether another run is needed:

compare length of array with the number countProducts generated
determine the number of runs on forehand by dividing the number countProducts generated by 1000 (ceil())
compare last found name with new last found name

I just don't know how to loop and where. I assume the solution is found by adding a helper function, but when I try that I get caught in values not being available and so on.

You don't have to solve my problem, but I would be very grateful if some one could supply an example of the needed structure or some internet source that describe this structure. The examples I found don't use values from the former runs.

Answer 1

BUILDARGS did not return a HASH reference

Answer 2

为了更好地理解代码，我在需要的地方添加了注释。随便问什么。

注意：此代码未经测试，可能无法按原样工作。这只是向您展示如何实际操作。

note1：您可能还想看看async-await，它们与promise一样，但是在语法上更加可读和清晰

let getProducts = function() {
  // return your promise, you may want to getProducts.then()
  return countProducts() 
    .then(function(number) {
      return getProductNames(number);
    })
    .catch(function(err) { // always put a catch
       console.log('there was an error', err)
    })
}


// make your getProductsName take in number value
// the name it takes is empty by default, we will provide name when we recursively call it
let getProductNames = function(number, name = ''){
  // check if your number is less than -1000 here , why ? keep reading the code
  if (number < -1000) return [];
  const nameCount = 1000;
  let names = []
  return callAPI({name, nameCount})
    .then(function(namesFromCallAPI) {
       names = names.concat(namesFromCallAPI); // you can concat two arrays at once
       // I do not know why you are poping the names, since it will mutate the array
       // use any one as per requirement
       let newName = names.pop();
       // OR let newName = names[names.length-1]; which will not mutate the array
       // recursively call the function by decreasing it by your nameCount
       // when your number is 500, it can still call but the result will be -500, which will run
       // in the next iteration -500-1000 will be -1500 which is < -1000 (explanation of base condition)
       return getProductNames(number - nameCount, newName)
    })
    .then(function(res) {
      // the result from getProductNames is again concatinated to our names and returned
      return names.concat(res);
    })
    .catch(function(err) {
       // always put a catch in your chain
       console.log('There was an error in our recursive function', err);
    })
}


// make a separate function that would api call
// put any parameters that you may need to make customizable here
let callAPI = function(params) {
  return new Promise(function(resolve,reject) {
    xyz.api.checkProducts(params.name, params.nameCount, function(err, names){
      if (err){
        reject(err);
      } else {
        resolve(names);
      } 
    });
  })
}

Node JS promise - run function multiple times with parameter from former run

2 个答案: