Accessing and comparing JSON values

Question

Writing in AngularJS, I've made an $http request to a JSON file within a service and I need to write an if statement to check whether the last value is more or less than the value before. It will only work if I place variables beneath the for loop, and this shouldn't be case.

When I console.log the length or the array it returns 0. I'm not sure whether the issue lies with my array, for loop or if statement. How do I iterate over the objects in the JSON file and push these items into an array?

app.factory('fxRate', ['$http', '$q', function($http, $q){

    var factory = {};

    factory.getFx = function() {
        return $http.get('../json/mcfx.json');
    }

    return factory;

}]);

app.controller('dashboard', ['$scope', 'fxRate', function($scope, fxRate){

    $scope.dailyFx = function() {
        fxRate.getFx().then(function(response) {
            //handle response or data
            var rates = [];
            var rateData = response.data.fxrate;
            var last_el = rates[rates.length - 1];
            var prev_el = rates[rates.length - 2];            
            console.log(rates)
            for (var i in rateData) {
               rates.push(rateData[i].usdToEur)
            }

            if(last_el > prev_el) {
                console.log('greater'); //0.9786
            } else {
                console.log('lesser'); //0.9232
            }        
        });
    }

    $scope.dailyFx();

}])

{
    "fxrate": [
        {
            "usdToEur": "0.94",
            "date": "23/05/2017"
        },
        {
            "usdToEur": "0.9232",
            "date": "24/05/2017"
        },
        {
            "usdToEur": "0.9786",
            "date": "25/05/2017"
        }       
    ]
}

Which variables are you talking about when you say : "It will only work if I place variables beneath the for loop" ? — JeanJacques
– JeanJacques, Commented May 24, 2017 at 14:25

Mike Feltman · Accepted Answer · 2017-05-24 14:41:12Z

2

You're accessing rates.length and trying to address it like there should be members in it after you've assigned [] to it, which makes it an empty array.

I think you want something more like this:

app.controller('dashboard', ['$scope', 'fxRate', function($scope, fxRate){

    $scope.dailyFx = function() {
        var rates = [];
        var rateData = [];
        var last_el
        var prev_el

        fxRate.getFx().then(function(response) {
            //handle response or data

            rateData = response.data.fxrate;
            console.log(rates)
            for (var i in rateData) {
               rates.push(rateData[i].usdToEur)
            }
            last_el = rates[rates.length - 1];
            prev_el = rates[rates.length - 2];            

            if(last_el > prev_el) {
                console.log('greater'); //0.9786
            } else {
                console.log('lesser'); //0.9232
            }        
        });
    }

    $scope.dailyFx();

}])

You're basically doing it correctly, just in the wrong order. In your code, the rates array will always be empty when these 2 lines execute:

var last_el = rates[rates.length - 1];

var prev_el = rates[rates.length - 2];

edited May 24, 2017 at 14:41

answered May 24, 2017 at 14:25

Mike Feltman

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3 Comments

Patrick McDermott Over a year ago

This is what I did and it worked, but I always thought it was best practice to keep all variables at the top, so just wondered if there was a more efficient way of writing the script to keep them there. Thanks for your time anyway

Mike Feltman Over a year ago

You can declare the variables at the top if you like but you still have to assign values to them in the appropriate order. I can edit the answer to reflect that, but if this is what you did, then why did you accept another answer?

Patrick McDermott Over a year ago

Before I posted this question I did what you've answered with, but what I was looking for was something similar to @IAmKale's answer. If you could edit your answer to show that, that would be perfect

IAmKale · Accepted Answer · 2017-05-24 14:39:50Z

1

The issue is your then() statement. You define last_el and prev_el before your rates array is ever populated. Try this:

fxRate.getFx().then(function(response) {
  // Extract the USD to EUR rate from the returned response
  var rates = response.data.fxrate.map(function(rate) {
    return rate.usdToEur;
  });
  console.log(rates);

  // Grab the last and previous elements
  var last_el = rates[rates.length - 1];
  var prev_el = rates[rates.length - 2];            

  if(last_el > prev_el) {
      console.log('greater'); //0.9786
  } else {
      console.log('lesser'); //0.9232
  }        
});

You should now see something in the console:

edited May 24, 2017 at 14:39

answered May 24, 2017 at 14:27

IAmKale

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1 Comment

Patrick McDermott Over a year ago

Brilliant! Exactly what I needed

Conan · Accepted Answer · 2017-05-24 14:27:45Z

1

Try this:

$scope.dailyFx = function() {
    fxRate.getFx().then(function(response) {
        //handle response or data
        var rates = [],
           rateData = response.data.fxrate,
           last_el, prev_el;

        for (var i in rateData) {
           rates.push(rateData[i].usdToEur)
        }

        if (rateData.length > 1) {
            last_el = rates[rateData.length - 1];
            prev_el = rates[rateData.length - 2];            
        }

        if (last_el > prev_el) {
            console.log('greater'); //0.9786
        } else {
            console.log('lesser'); //0.9232
        }        
    });
}

answered May 24, 2017 at 14:27

Conan

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