Create a setter for a local variable in a Javascript object

Question

I have the following code

var loyaltyObject = (function () {
  var data = null, vm, getLoyaltyUrl;

  function getData() {
    $.ajax({
      type: 'POST',
      url: getLoyaltyUrl,
      contentType: 'application/json; charset=utf-8',
      dataType: 'json',
      success: function (resp) {
        data = resp;
      },
      error: function (resp) {
        console.log('Error fetching offers!');
        console.log(resp);
      }// error(resp)
    });// $.ajax()  
  }

...

  vm = {
    getData: getData,
    getLoyaltyUrl: getLoyaltyUrl
  };

  return vm;
}());

on document.ready I call

function Init() {
    window.loyaltyObject.getLoyaltyUrl = '@Url.Action("GetLoyaltyData", "Orders")';
    window.loyaltyObject.getData();
}

window.loyaltyObject.getLoyaltyUrl is indeed the url but the internal getLoyaltyUrl is still undefined.

I read the following return a variable as a property about setting up a getter, but how would I perform a setter, what is the this or value I would be setting?

Also would it be comparable on most browsers?

FWIW, I think there is an expectations that properties which start with get... are actually functions. — Felix Kling
– Felix Kling, Commented Jul 10, 2017 at 23:47
What's the reason for not making the URL a parameter of getData? — Felix Kling
– Felix Kling, Commented Jul 10, 2017 at 23:50
vm has getLoyaltyUrl as a (public) property, no need for a setter. Or do you want to set it on loyaltyObject? — david25272
– david25272, Commented Jul 11, 2017 at 0:00
Just use the this.getLoyaltyUrl property inside the method and drop the local variable. — Bergi
– Bergi, Commented Jul 11, 2017 at 0:51
Making the URL a parameter seems to be more natural to me. It's more expressive. "I want to load data from this URL" vs "Set this property to a URL and then get the data". — Felix Kling
– Felix Kling, Commented Jul 11, 2017 at 18:08

charlietfl · Accepted Answer · 2017-07-11 00:02:00Z

2

You are assigning the value to vm.getLoyaltyUrl not to the private variable getLoyaltyUrl. That variable has no inheritance from the object vm so it never ever gets defined in your code

Just change:

url: getLoyaltyUrl

to

url: vm.getLoyaltyUrl

Simplified example

var loyaltyObject = (function () {
  var data = null, vm;

  function getData() {
   // switched out the ajax for a simple console.log()
   console.log(vm.getLoyaltyUrl)
  }

  vm = {
    getData: getData,
    getLoyaltyUrl: null
  };

  return vm;
}());
// following is exactly what you have
function Init() {
    window.loyaltyObject.getLoyaltyUrl = '@Url.Action("GetLoyaltyData", "Orders")';
    window.loyaltyObject.getData();
}

Init()

answered Jul 11, 2017 at 0:02

charlietfl

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Comments

Felix Kling · Accepted Answer · 2017-07-10 23:46:27Z

1

but how would I perform a setter, what is the this or value I would be setting?

You would simply assign to the variable getLoyaltyUrl:

vm = {
  // ...
  set getLoyaltyUrl(value) {
    getLoyaltyUrl = value;
  },
}

You wouldn't use this in your case. value is the value assigned to the property.

answered Jul 10, 2017 at 23:46

Felix Kling

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Comments

T4rk1n · Accepted Answer · 2017-07-11 00:52:02Z

0

I don't think there's any need for a custom property here. But you can look into Object.defineProperty or it's Reflect counterpart to change objects properties on the fly.

Object.defineProperty(obj, 'getLoyaltyUrl', {
    set: (value) => {
        // do something here, better be worth it.
    },
    get: () => {}
})

answered Jul 11, 2017 at 0:52

T4rk1n

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