Unique strings/symbols practicality

_library.js

(function(global){
    var findIndexPropName = String.unique();
    var shufflePropName = String.unique();

    Array.prototype[findIndexPropName] = function(){ /*...*/ };
    Array.prototype[shufflePropName] = function(){ /*...*/ };

    global.arraySupplementals = {
        findIndex: findIndexPropName,
        shuffle: shufflePropName
    };

})(this)

client.js

(function(global){

    var {findIndex, shuffle} = global.arraySupplementals;

    var myArray = [/*...*/];
    function f(){ /*...*/ }
    
    console.log(myArray[findIndex](f)
    myArray[shuffle]();
    console.log(myArray[findIndex](f))

})(this);