Is there any way to prevent a user from overriding a native function?
Example:
var getRand;
(function(){
'use strict';
getRand = function(){
return Math.random();
}
})();
getRand(); //gives a nice random number
After the page has loaded, overriding in console.
Math.random = function (){ return 0 };
getRand(); //gives 0 :(
Is there any way to prevent native functions from being overridden? Maybe with CSP or sealing the Object... is this even possible?
In fact, you can use Object.freeze(Math):
The Object.freeze() method freezes an object: that is, prevents new properties from being added to it; prevents existing properties from being removed; and prevents existing properties, or their enumerability, configurability, or writability, from being changed. In essence the object is made effectively immutable. The method returns the object being frozen.
Object.freeze(Math);
// This won't work or it won't replace
// the function with the whole string...
Math.random = "hello world";
Unless any other library could be relying on extending or modifying Math (for example, maybe a polyfill might need to add a function or whatever to Math but as I said before, it's just a possible issue when freezing a built-in object...).
...using Object.defineProperty(...) to modify an existing property descriptor:
Object.defineProperty(Math, "random", {
configurable: false,
writable: false
});
freeze is not part of Object.prototype btw. It's a direct member of Object.
Object.freeze is equivalent to setting all property descriptors to { writable: false, configurable: false }...