async loop

loop.js

// This will make the requests one at a time, not all at once,
// but everything after will still be called because it's async
// add tags to post
const tags = post.tags
post.tagNames = []

const loop = i => {
  const tagnum = tags[i]

  rp(tagUrl + tagnum).then(data => {
    if (data) {
      var x = JSON.parse(data)
      post.tagNames.push(x.name)
    } else {
      return new error('failed to get tag names')
    }

    if (tags[i + 1]) {
      loop(++i)
    }
  })
}

loop(0)


// This will be blocking, so anything after calling getTagNames
// will not be executed
const getTagNames = tags => {
  const tagNames = []

  return new Promise((resolve, reject) => {
    const loop = i => {
      const tagnum = tags[i]
  
      rp(tagUrl + tagnum).then(data => {
        if (data) {
          var x = JSON.parse(data)
          tagNames.push(x.name)
        } else {
          return reject(new error('failed to get tag names'))
        }
  
        if (tags[i + 1]) {
          loop(++i)
        } else {
          resolve()
        }
      })
    }
  
    loop(0)
  })
}

// Get the names, then do something afterwards
getTagNames(post.tags).then(names => {
  post.tagNames = names
})


// Or using async/await, which is the cleanest IMO
// The function this is in has to be async
const getTagNames = async tags => {
  const tagNames = []

  for (var i = 0; i < tags.length; i++) {
    const tagnum = tags[i]
    let data
    
    try {
      // This is the magic that makes it blocking
      data = await rp(tagUrl + tagnum)
    } catch (err) {
      throw err
    }
    
    if (data) {
      var x = JSON.parse(data);
      tagNames.push(x.name);
    } else {
      throw new error('failed to get tag names');
    }
  }

  return tagNames
}

// Do something
post.tagNames = getTagNames(post.tags)
// This won't happen until the above is finished