Ensure for loop waits until moving onto next item in JavaScript

Question

Firstly I appreciate that there are many answers out there explaining this topic but I just can't understand it at the moment.

I want to loop through a JavaScript object I have created and then perform various actions like making a request to an API and then storing some data in Redis.

This is what I have so far

const params = { "handle1": { "screen_name": "handle1", "hash_tag": "#hashtag1"},
             "handle2": { "screen_name": "handle2", "hash_tag": "#hashtag2"} }

for (const k of Object.keys(params)) {
  console.log("Searching for " + params[k]['screen_name'])

  client.get('statuses/user_timeline', { screen_name: params[k]['screen_name']})
  .then(function (tweets) {

    for (const key of Object.keys(tweets)) {
      const val = tweets[key]['text'];

      if(val.includes(params[k]['hash_tag'])) {
        console.log("Found")
        r_client.hset(params[k]['screen_name'], 'tweet_id', tweets[key]['id'], 'tweet_text', tweets[key]['text'], function (err, res) {
          console.log(res)
        });
        r_client.hgetall(params[k]['screen_name'], function(err, object) {
          console.log(object);
        });
     }
   }
   r_client.quit();
  })
  .catch(function (error) {
    throw error;
  });
}

When I run this the output is as follows

Searching for handle1
Searching for handle2
Found
0
{ tweet_id: '123456789',
  tweet_text: 'text found in tweet' }
Found
undefined
undefined

So straight away I have a problem in that the first loop hasn't event finished and it's moved onto the second loop.

I would like to run this in sequential order (if that's the best way), but more importantly I was hoping someone could break down my code and explain how I should be approaching this to have it run correctly.

The second loop is inside the definition of the first. If you need to run one then another consider putting them side by side. — evolutionxbox, Mar 21 '18 at 14:28
Rich, your questions are a bit noisy for a 7K user. We trim out "thanks" and "help appreciated" - you have 317 instances of the latter, which is a lot of work for volunteer editors. Please also refrain from giving voting advice - if people think your question is worth voting one way or the other, they will. Don't paint a target on your back. — halfer, Mar 21 '18 at 14:38
@halfer apologies, did not realise you guys did that. Always thought politeness went a long way, though no problem if these kind of civilities are unnecessary. Will refrain from doing this in the future — Richlewis, Mar 21 '18 at 14:43
Yep, a technical standard of writing is preferred here. References [here](https://meta.stackoverflow.com/q/260776) and [here](https://meta.stackoverflow.com/q/288160), and there's probably others lurking on _Meta_! — halfer, Mar 21 '18 at 15:05

score 0 · Answer 1 · answered Mar 21 '18 at 14:31

0

const tweets = await client.get(...) should do the trick.

answered Mar 21 '18 at 14:31

Gabriel Bleu

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Hi, doesnt work, would you be able to elaborate on your answer please – Richlewis Mar 21 '18 at 15:25
@Richlewis do you have any error ? If you await, each loop iteration should queue. – Gabriel Bleu Mar 21 '18 at 15:52
Nodejs supports async/await from version 7.6 [see](https://stackoverflow.com/questions/37815790/syntaxerror-unexpected-token-function-async-await-nodejs) – Gabriel Bleu Mar 21 '18 at 16:17

Sebastian Speitel · Answer 2 · 2018-03-21T15:29:30.817

Under the condition that .get(), .hset() and hgetall() return Promises this should pause the execution until all functions have resolved:

const params = {
  "handle1": {
    "screen_name": "handle1",
    "hash_tag": "#hashtag1"
  },
  "handle2": {
    "screen_name": "handle2",
    "hash_tag": "#hashtag2"
  }
}
async function search(params) {
  for (const k in params) { //for..in goes through the keys
    console.log("Searching for " + params[k]['screen_name'])

    const tweets = await client.get('statuses/user_timeline', {
      screen_name: params[k]['screen_name']
    });

    for (const key in tweets) { //same loop
      const val = tweets[key]['text'];

      if (val.includes(params[k]['hash_tag'])) {
        console.log("Found")
        await r_client.hset(params[k]['screen_name'], 'tweet_id', tweets[key]['id'], 'tweet_text', tweets[key]['text'], (err, res) => {
          console.log(res)
        });
        await r_client.hgetall(params[k]['screen_name'], (err, object) => {
          console.log(object);
        });
      }
    }
    r_client.quit();
  }
}

search(params);

Forget that `await` can only be used in async functions. Edited it. — Sebastian Speitel, Mar 21 '18 at 15:30
For larger loops, `await Promise.all` or Bluebird's `Promise.map` might be suited better than awaiting each promise on its own. — k0pernikus, Mar 21 '18 at 15:46

Ensure for loop waits until moving onto next item in JavaScript

2 Answers2