More Questions About Asynchronous Programming

[p0_boy]

Hello again, e'rybody-

I have the following JSON object, stored in a variable ($gameSystem._ipLookupJSON):

Each of the keys in the object above is a URL.

I am trying to write a function ($._findService()) that:

1. Goes through each key one by one,
2. Sends that key to another function ($._urlExists()), which checks if the URL is valid / responsive,
3. If it is- create a new variable object / array with only that key and its elements (City, Country, IP); and then-
4. "breaks" the function because it has already found a working URL, returning the new object that was created.

Here is $._findService(), as I have it so far:

$._findService = function(json_data) {
    Object.keys(json_data).some(async function(k){
        var check_for = "http://" + k;
        var url_check = await $._urlExists(check_for);
        url_check.then(function(value){
            if (value === true) {
                var service_to_use = json_data[k];
                return service_to_use;
            };
        });
    });
};

And here is $._urlExists():

    $._urlExists = function(url_to_check) {
      // check if string  is valid url format, source: https://stackoverflow.com/a/5717133
      var pattern = new RegExp('^(https?:\\/\\/)?'+ // protocol
      '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|'+ // domain name
      '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address
      '(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*'+ // port and path
      '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string
      '(\\#[-a-z\\d_]*)?$','i'); // fragment locator
      if (!!pattern.test(url_to_check) == true) {
          return new Promise(function(resolve, reject) {
              // check if url exists, source: https://stackoverflow.com/a/24297372
              var reader = new XMLHttpRequest();
              reader.open('get', url_to_check, true);
              reader.onreadystatechange = (function() {
                  if (reader.readyState === 4) {
                      //check to see whether request for the file failed or succeeded
                      if ((reader.status == 200) || (reader.status == 0)) {
                          return resolve(true);
                      } else {
                          return resolve(false);
                      };
                  };
              });
              reader.send(null);
          });
      };
    };

Unfortunately, I am running into the same problem I had in my previous post, where (because $._urlExists() uses asynchronous programming) $._findService() just returns an undefined value rather than the new array.

As you can see, I am trying to use async/await to avoid this... but I am not sure if I am doing it correctly. There could be other mistakes that I am making, I have just been staring at these particular lines of code for so long I feel as if I am at my wit's end already.

I am hoping that somebody brighter than me can throw me a bone and let me know how I can get this working.

As always, thanks in advance and have a great weekend!


Addendum
I guess I was asking too heady of a question.

Anyway, reading and Googl'ing led me to a solution on flaviocopes.com which made me break down $._findService() into three different functions:

    const isServiceAvailable = async url_to_check => {
      console.log(url_to_check);
      return await subaybay.an._urlExists("http://" + url_to_check);
    };
 
    const checkServices = async(json_data) => {
        return await Promise.all(Object.keys(json_data).map(url_to_check => isServiceAvailable(url_to_check)));
    };
 
    $._findService = function(json_data) {
        var url_check = checkServices(json_data);
        url_check.then(function(values) {
            for (i = 0; i < values.length; i++) {
                if (values[i] === true) {
                    service_to_use = new Array();
                    service_to_use.push(Object.keys(json_data)[i]);
                    console.log(service_to_use);
                    return service_to_use;
                };
            };
        });
    };

I am still running into problems in the last part of $._findService()-

                if (values[i] === true) {
                    service_to_use = new Array();
                    service_to_use.push(Object.keys(json_data)[i]);
                    console.log(service_to_use);
                    return service_to_use;
                };

I am having problems creating a new variable object / array with the working URL and its elements (City, Country, IP); and getting it to return the new array.

However, I will toil on and probably get it soon. Stay tuned.

Addendum 2:
I am so close.

    $._findService = function(json_data) {
      var url_check = checkServices(json_data);
      url_check.then(function(values) {
        for (i = 0; i < values.length; i++) {
          if (values[i] === true) {
            var service_to_use = new Promise(function(resolve, reject) {
              var result = [];
              console.log('json_data[Object.keys(json_data)[i]]:');
              console.log(json_data[Object.keys(json_data)[i]]);
              result.push(json_data[Object.keys(json_data)[i]]);
              console.log('Object.keys(json_data)[i]:');
              console.log(Object.keys(json_data)[i]);
              result.unshift(Object.keys(json_data)[i]);
              resolve(result);
            });
            service_to_use.then(function(value) {
              console.log('value:');
              console.log(value);
              return value;
            });
          };
        };
      });
    };

I just can't get $._findService() to return the service_to_use result. Sigh.


Addendum 3
filipe at stackoverflow was able to give me the solution I was looking for:

const isServiceAvailable = async url_to_check => {
    console.log(url_to_check);
    return await subaybay.an._urlExists("http://" + url_to_check);
};

const checkServices = async(json_data) => {
    return await Promise.all(Object.keys(json_data).map(url_to_check => isServiceAvailable(url_to_check)));
};

$._findService = async(json_data) {
    const values = await checkServices(json_data);

    for (let i = 0; i < values.length; i++) {
        if (values[i] === true) {
            const result = [];
            result.push(json_data[Object.keys(json_data)[i]]);
            result.unshift(Object.keys(json_data)[i]);
            console.log(result);
            return result;
        }
    }
};

And then use:

const result = await $._findService($gameSystem._ipLookupJSON);

Phew.

 

[Kes]

[closed]IgnoreMe[/closed]