Nodejs loop through same API with different parameters

Question

I trying to loop through same API result and if the API result is NULL then I want loop through it again few times (i.e 4-5 times) with different parameters and if it's reached the 5th time. I want to exit the loop. The code I'm trying is see below:

var roads = 1000;
var findResult = true;
var loop = 0;

while (findResult) {
  result = APIResult(rarray, roads);
  if (result !== null) {
    findResult = false; // stop the loop
  } else if (loop == 5) {
    findResult = false; // stop the loop
  } else {
    roads = roads * 10;
    loop++;
  }
}

function APIResult(rarray, roads) {
  request.post(
      env.TEST_URL + 'test/',
      {
        json: {
          //...
          roads: roads,
          //..
        },
      },
      function(error, response, body) {
        if (!error && response.statusCode == 200) {
          return JSON.parse(body.rows[0].result);
        }
      });
}

I'm even tried adding Q promise but didn't worked, any idea how to do it?

You are checking the value of APIResult, which seems to be async method. use a callback and then a timeout maybe to wait for sometime before hitting the API again. — Prabodh M
– Prabodh M, Commented Jul 4, 2017 at 11:19

galkin · Accepted Answer · 2017-07-04 11:27:41Z

1

Your APIResult function doesn't return anything. This function is asynchronous, so it should return promise or use a callback.

Your code result = APIResult(rarray, roads); sets to result variable undefined value. I think, async/await style for implementing asynchronous JS features will work for you.

Current last Node.js version is 8.1. It has native support for async/await. There is an example, how you can implement your code:

async function main() {
  var roads = 1000;
  var findResult = true;
  var loop = 0;
  while (findResult) {
    try {
      result = await APIResult(rarray, roads);
    } catch (e) {
      //APIResult reject promise branch
    }

    if (result !== null) {
      findResult = false; // stop the loop
    } else if (loop == 5) {
      findResult = false; // stop the loop
    } else {
      roads = roads * 10;
      loop++;
    }
  }
}

async function APIResult(rarray, roads) {
  return new Promise((res, rej) => {
    request.post(
        env.TEST_URL + 'test/',
        {
          json: {
            //...
            roads: roads,
            //..
          },
        },
        function(error, response, body) {
          if (error) return rej(error);
          if (response.statusCode === 200) return res(JSON.parse(body.rows[0].result));
        });
  });
}

main();

answered Jul 4, 2017 at 11:27

galkin

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3 Comments

FR STAR Over a year ago

Thanks for your reply @galkin, then above code won't work in the node v6.11.0?

FR STAR Over a year ago

Tried your code, but for some reason there is no records returning now from the API response. I even placed a debug code in the request call back function and looks like it's not even reaching there.

galkin Over a year ago

Yes, this code will not work on 6.11 Node.js without babel (babeljs.io). As i wrote, for you will be the best solution use async/await. Or you should learn Promises/callbacks/generators staff.

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