Global Variables JS - Component Controller

Question

So I have a global variable defined in my code and it is throwing an error. The error is

Failed to save undefined: 0Ad1F0000000meq: org.auraframework.util.json.JsonStreamReader$JsonStreamParseException: Only functions are allowed in javascript controllers [3, 17]: '10': Source

My code is in JavaScript. It is a controller for my component. I want to declare a global variable but am I declaring it correctly?

Simplified code:

({
  x: 10,   /* Global variable */
  y: 15    /* Global variable */

  function1 : function(..){
  },
  ....
})

Answer 1

You can declare those variables in helper and access them like that:

({
    x: 10,
    y: 15,
    someHelperFunction: function() {
        console.log(this.x);
    }
})

or from the controller:

({
    someControllerFunction: function(component, event, helper) {
        console.log(helper.x);
    }
})

Answer 2

That's not possible within lightning framework.

Unlike JavaScript, we have to create aura:attribute in component; which can be used for storing data available to client side controller and helper globally.

Basic example

<aura:component>

    // attribute
    <aura:attribute name="recordId" type="String"/>

    // other code
</aura:component>

With this recordId attribute is registered for the component and can be accessed by v.recordId property in client side helper and controller.

// getter
component.get("v.recordId");
// setter
component.set("v.recordId", "record id value");

One can use a function in helper or controller which returns value but using aura:attribute is much cleaner.