async-test.js

/* 
Task: 
- request all files asynchronously
- print them out in order of file1 > file2 > file3
- print result as soon as it returns
- after all done, print "Completed!"
- only rely on promise without any promise helper (i.e Promise.all)
*/

// ======= implementation 1 ======== //

const fetchedFiles = {
    file1: { status: 'NOT_FETCHED', data: null },
    file2: { status: 'NOT_FETCHED', data: null },
    file3: { status: 'NOT_FETCHED', data: null },
}

let fileCount = 0;

function fakeAjax(url,cb) {
    var fake_responses = {
        "file1": "The first text",
        "file2": "The middle text",
        "file3": "The last text"
    };
    var randomDelay = Math.round(Math.random() * 1E4);

    console.log("Requesting: " + url);

    setTimeout(function(){
        cb(fake_responses[url]);
    },randomDelay);
}

function output(file) {
    file.status = 'PRINTED'
    console.log(file.data);
}

function checkStatus(statusKey) {
    const x = Object.values(fetchedFiles).reduce((acc, obj) => {
        if (obj.status === statusKey) {
            return acc + 1
        }
        return acc;
    }, 0)
    return x
}

function getFile(filename) {
  /* body of getFile? */
  fakeAjax(filename, (data) => {
    fileCount++;
    fetchedFiles[filename].status = 'FETCHED';
    fetchedFiles[filename].data = data;

    for (const key of Object.keys(fetchedFiles)) {
        if (fetchedFiles[key].status === 'NOT_FETCHED') {
            continue;
        } else if (fetchedFiles[key].status === 'PRINTED') {
            continue;
        } else {
            output(fetchedFiles[key]);
        }
    }

    // if (fileCount === checkStatus('PRINTED')) {
    //     return console.log('Completed!')
    // }

    // if (fileCount === 1) {
    //     return output(fetchedFiles[filename]);
    // }
  })
}

// getFile('file2');
getFile('file3');
getFile('file1');

// ======= implementation 2 ======== //

const NOT_FETCHED = 'NOT_FETCHED';
const FETCHED = 'FETCHED';
const PRINTED = 'PRINTED';

// alternative: use single object that stores content and status instead of two arrays
const filesStatus = Array(3).fill(NOT_FETCHED); // [NOT_FETCHED, NOT_FETCHED, NOT_FETCHED]
const filesContent = Array(3).fill(null);

const fetchFileCallback = (content, fileId) => {
  // update file status and content
  filesStatus[parseInt(fileId) - 1] = FETCHED;
  filesContent[parseInt(fileId) - 1] = content;

  // print if applicable
  for (let i = 0; i < 3; i++) {
    if (filesStatus[i] === NOT_FETCHED) {
      break;
    } else if (filesStatus[i] === PRINTED) {
      continue;
    } else if (filesStatus[i] === FETCHED) {
      print(filesContent[i]);
      filesStatus[i] = PRINTED;
      if (i === 2) print('Done');
    }
  }
}


function fetchFile(url, cb) {
  var responses = {
    "file1": "Content 1",
    "file2": "Content 2",
    "file3": "Content 3",
  };

  var randomDelay = Math.round(Math.random() * 1000);

  setTimeout(function wait() {
    cb(responses[url], url[url.length - 1]);
  }, randomDelay);

}
function print(msg) {
  console.log(msg);
}
function getFile(filename) {
  fetchFile(filename, fetchFileCallback);
}

getFile('file1')
getFile('file2')
getFile('file3')

// ========= implemenation 3 ========= //

import { addListener } from "cluster";

const randomDelay = () => Math.floor(Math.random() * 10) + 1
const returnedData = {
    file1: null,
    file2: null,
    file3: null
}

function fetchFile(url, cb) {
    const data = {
        "file1": "content1",
        "file2": "content2",
        "file3": "content3"
    }

    setTimeout(() => {
        cb(url, data[url])
    }, randomDelay())
}

class EventEmitter {
    listeners = [];
    internalValue = 0;

    constructor () {
        this.internalValue = 0;
    }

    emit(payload) {
        for (const listener of this.listeners) {
            listener(payload)
        }
    }

    addListener(callback) {
        this.listeners.push(callback)
    }
}

function getFile(filename) {
    fetchFile(filename, (url, data) => {
        // if url name is file 1 should always return first
        if (url === "file1") {
            returnedData[url] = data
            console.log(data)
            return
        }

        // if url is file 2 should check if file 1 has been logged
        // if not, wait for file 1 to be logged

        // if (url === "file1") {
        //     returnedData[url] = data
        //     return console.log(data)
        // } else if (url === "file2") {
        //     returnedData[url] = data
        //     if (returnedData.file1) {
        //         return console.log(returnedData.file1, data)
        //     }
        // } else if (url === "file3") {
        //     returnedData[url] = data
        //     if (returnedData.file1 && returnedData.file2) {
        //         return console.log(returnedData.file1, returnedData.file2, data)
        //     }
        // }
    })
}

getFile("file1")
getFile("file2")
getFile("file3")