TFL Tracker App

Goals

  • quick interface with typeahead for users to find information with ease on low quality networks
  • show incoming trains and information on scheduling
  • bootstrapped and easy to develop/extend

Challenges

TFL's API is ancient and uses a variation of XML. Also, it doesn't send any X-headers for authorization and content access control, so a proxy server is necessary (supplied in both python and Node.js) to get this information, process and provide headers, and serve up to the Vue.js web app.

Prerequisites

  • NodeJS (prefer latest)
  • Express router (npm install express)
  • Node XMLHTTPRequest (npm install xmlhttprequest)

Usage

Start proxy server:

node proxy/server.js

(listens on 8080, forward server HTTP traffic here)

Direct visitors to src/index.html (or if using Github Pages then docs/index.html).

Github Pages: Put the precommit hook into git hooks folder (cat pre-commit.hook > .git/hooks/pre-commit). Then on commit it'll create a brand new docs/ folder for you with all the client files from src/ (index.html/.js, style.css).

Draft Spec

  • Vue frontend
    • typeahead for station
    • color coded selection for line
    • display result by platform
  • Express backend
    • query TFL xml api, parse train info

Draft Flow:

App Loads

  | User chooses station

  -> | User chooses line

    -> | Vue client contacts Express proxy with station+line

      -> | proxy forwards XML from TFL API to Vue client

        -> | Vue client displays result

Known Issues

  • TFL doesn't send COORS, as a result a proxy server is put in place. (I have contacted TFL about their API)
  • Using a synchronous XMLHTTPRequest can have a negative impact on user experience; this is a known issue, but when in underground the poor signal and wireless can cause unexpected drops, and an asynchronous request here could break and cause a race condition due to poor wireless connection. Willfix in later release.
  • Using an XMLHTTPRequest polyfill as opposed to fetch, will fix at a later point and used only to provide the same syntax used on client. Hopefully at a later point TFL will send COORS headers and the proxy snippet can be placed back into the client.

Credits

  • Using Bootstrap 3 for quick UI
  • TFL API provides data
  • Using Express for proxy server
  • Using Vue script-based approach
  • Favicon from Flaticon, designed by Freepik (source image)

Quick Spec

  • needs to allow picking of station and line
  • show incoming trains to station
  • show eta, final destination, current location of train
  • quick to load
  • updated in realtime, using TFL api

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