Does this code make my Number "save"?

Question

Hey,

it's difficult to write in the title what I want. So sorry, if the title doesn't make much sense ;)

I wanted to create a variable or container that contains a number as a value. The value has to be a number and I want to get notified if it got changed. I came up with the following idea:

const saveNumber = (function () {

var numberValue = null;

return {

set value(value){
console.warn('Number was changed!');
if(typeof value !== 'number') {
throw 'Value has to be a number!';
return;
}
numberValue = value;
},

get value(){
return numberValue;
}
}
})();

This leads to the following behaviour:

saveNumber.value = 5; // "Number was changed!"

saveNumber.value = "Strings don't work"; // throws 'Value has to be a number!'

console.log(saveNumber.value); // 5

So in my opinion I created some kind of a "save" number or value. I call it saved since the value can't be manipulated directly or in other words without using the setter function. In addition it's save because I get notified as soon as the value gets changed.

My question is: Does this code make sense and does it really lead to the above described behaviour? Or is the still a way to change the numberValue without using the getter function?

Thank you!

Answer 1

In your code example the value is in the closure of the returned object and inaccessible from the outside.

Take a look at Object.defineProperty()
(https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty)
Ist's a way to define a property directly with getter and setter.

and be aware that NaN is also of type number.

Answer 2

Hey, thanks for your answer!

You said: "In your code example the value is in the closure of the returned object and inaccessible from the outside."

That's the whole point of my code :) I think I didn't explain very well what I wanted to achieve...

I'll have a look at Object.defineProperty() since I don't know it yet. Thanks again!