[Express] Level 3: Massaging User Data

Flexible Routes

Our current route only works when the city name argument matches exactly the properties in the cities object. This is a problem. We need a way to make our code more flexible.

Inside our route, call the parseCityName() function passing in the name parameter. Assign the return value to the new variable called cityName.

var cityName = parseCityName(request.params.name);

function parseCityName(name) {
  var parsedName = name[0].toUpperCase() + name.slice(1).toLowerCase();
  return parsedName;
}

Now, using the city name returned from the parseCityName() function, lookup the corresponding description using the cities object and store it in the correct variable that will make the rest of the function work as intended.

  var cityName = parseCityName(request.params.name);
  var cityInfo = cities[cityName];

var express = require('express');
var app = express();

var cities = {
  'Lotopia': 'Rough and mountainous',
  'Caspiana': 'Sky-top island',
  'Indigo': 'Vibrant and thriving',
  'Paradise': 'Lush, green plantation',
  'Flotilla': 'Bustling urban oasis'
};

app.get('/cities/:name', function (request, response) {
  var cityName = parseCityName(request.params.name);
  var cityInfo = cities[cityName];

  if(cityInfo) {
    response.json(cityInfo);
  } else {
    response.status(404).json('City not found');
  }
});

function parseCityName(name) {
  var parsedName = name[0].toUpperCase() + name.slice(1).toLowerCase();
  return parsedName;
}

app.listen(3000);

Dynamic Routes I

Which Express function maps placeholders to callback functions, and is commonly used for running pre-conditions on Dynamic Routes?

Answer:

app.param();

Dynamic Routes II

Whenever we use our name parameter we want to parse it a specific way. Let's clean up our existing code so that all routes with a name parameter get the same special handling.

Call app.param() to intercept requests that contain an argument called'name'. Remember app.param() takes a callback function as its second argument, which uses the same signature as a middleware.

var express = require('express');
var app = express();

app.param('name', function(request, response, next){

});

Inside the app.param() callback function, call the parseCityName() function with the submitted name parameter. Set the return value to a new property in the request object called cityName.

app.param('name', function(request, response, next){
    request.cityName = parseCityName(request.params.name);
});

Finally, call a function that moves processing to the next function in the stack.

app.param('name', function(request, response, next){
  request.cityName = parseCityName(request.params.name);
  next();
});

var express = require('express');
var app = express();

var cities = {
  'Lotopia': 'Rough and mountainous',
  'Caspiana': 'Sky-top island',
  'Indigo': 'Vibrant and thriving',
  'Paradise': 'Lush, green plantation',
  'Flotilla': 'Bustling urban oasis'
};

app.param('name', function(request, response, next){
    request.cityName = parseCityName(request.params.name);
  next();
});

app.get('/cities/:name', function (request, response) {
  var cityInfo = cities[request.cityName];
  if(cityInfo) {
    response.json(cityInfo);
  } else {
    response.status(404).json("City not found");
  }
});

function parseCityName(name){
  var parsedName = name[0].toUpperCase() + name.slice(1).toLowerCase();
  return parsedName;
}

app.listen(3000);

Dynamic Routes III

The following code has a Dynamic Route that takes a year as an argument and returns the city created in that year. The problem with our current implementation is that it breaks when invalid data is sent on client requests. Let's add some basic validation.

Call a function that intercepts Dynamic Routes with the 'year' param.

app.param('year', function(request, response, next){

});

Inside of that function, use the isYearFormat() function to check whether the year parameter is in a valid format. If so, then move processing to the next function in the stack.

  if(isYearFormat(request.params.year)){
    next();
  }

If the year parameter is not in a valid format, then respond with a 400 HTTP status code and a JSON message 'Invalid Format for Year'.

app.param('year', function(request, response, next){
  if(isYearFormat(request.params.year)){
    next();
  }else{
      response.status(400).json('Invalid Format for Year');
  }
});

var express = require('express');
var app = express();

app.param('year', function(request, response, next){
  if(isYearFormat(request.params.year)){
    next();
  }else{
      response.status(400).json('Invalid Format for Year');
  }
});

var citiesYear = {
  5000: 'Lotopia',
  5100: 'Caspiana',
  5105: 'Indigo',
  6000: 'Paradise',
  7000: 'Flotilla'
};

function isYearFormat(value) {
  var regexp = RegExp(/^d{4}$/);
  return regexp.test(value);
}

app.get('/cities/year/:year', function(request, response) {
  var year = request.params.year;
  var city = citiesYear[year];

  if(!city) {
    response.status(404).json("No City found for given year");
  } else {
    response.json("In " + year + ", " + city + " is created.");
  }
});

app.listen(3000);

Dynamic Routes IV

With the proper validations in place for the following code, what would the output be for a GET request to /cities/year/500?