How to reset prototypes of JavaScript primitives [duplicate]

Question

A lot of the time, I write JavaScript that runs with other scripts or that may contain other scripts. Sometimes these scripts might have changed the prototypes for the primitive objects that I might be using in my code.

Is there a way I can declare my primitive datatypes in JavaScript so that it will reset the prototype if it has been modified? Or so that my scripts would run in a separate scope where the prototype of the primitive is not modified?

// evil script code modify primative on prototype
Boolean.prototype.toString = function() {
  return true;
}

let flag = false;
console.log(flag.toString());
// I would expect false to be printed, but because the prototype of the primative if overridden 
// the primative value would be wrapped with the Boolean object 
// and call the modified toString method and would output true.

Is there any way I can make sure my code is running in a separate scope, or any way I can declare my variables or reset the prototypes to avoid these types of issues?

Answer 1

You can freeze global object prototype but you need your script to run first. It will prevent modification.

I don't know how to freeze global function.

Object.freeze(String.prototype);
Object.freeze(Number.prototype);
Object.freeze(Boolean.prototype);
Object.freeze(Object.prototype);
Object.freeze(Array.prototype);
Object.freeze(Date.prototype);
Object.freeze(Math.prototype);
Object.freeze(Function.prototype);

// evil script code modify primative on prototype
Boolean.prototype.toString = function() {
  return true;
}

// For this I don't know how to freeze
window.parseInt = function(number) {
  return 'evil'
}

let flag = false;
console.log(flag.toString());

console.log(parseInt(1));