Is it possible to define a global constant from within a function in javascript

Question

I would like to be able to define a constant that is in the global scope from within a function. With a normal variable this would be possible by defining it outside the function and setting its' value from within the function as shown below:

var carType; 

function carType(){

    carType = 'Reliant Robin';

}

However you cannot define global variables without setting a value so this would not work with a constant, is there any way around this?

You might set a non-configurable property on the global object, but it's still a code smell. — CertainPerformance
– CertainPerformance, Commented Jan 2, 2019 at 2:17
@PatrickRoberts I know, "However you cannot define global variables without setting a value so the program will fail on the first line". I'm asking if there is any way around this — Henry Howeson
– Henry Howeson, Commented Jan 2, 2019 at 2:21
If you declare a variable before defining it, by definition it is not a constant, so your request makes no sense. — Patrick Roberts
– Patrick Roberts, Commented Jan 2, 2019 at 2:25
The short answer is no - you can't create a global const, let, or class identifier in global scope using declarations within a function or by using eval. I looked into the eval case for this answer regarding scope. — traktor
– traktor, Commented Jan 2, 2019 at 2:32

Trash Can · Accepted Answer · 2019-01-02 02:40:19Z

10

The answer is "yes", but it is not a typical declaration, see the code snippet below

function carType(){
  Object.defineProperty(window, 'carType', {
    value: 'Reliant Robin',
    configurable: false,
    writable: false
  });
}

carType();
carType = 'This is ignored'
console.log(carType);

answered Jan 2, 2019 at 2:40

Trash Can

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