override toString function in javascript

Question

hi im trying to override default Number wrapper toString function

(function() {
  let _toString = Number.prototype.toString;
  Number.prototype.toString = function() {
    console.log("Number ToString Called");
    _toString();
  };
})();

let b = new Number(5);
console.log(b);
document.writeln(typeof b);
document.writeln(b.toString());

question from:https://stackoverflow.com/questions/65875283/override-tostring-function-in-javascript

Answer 1

toString is a method, it receives the object to convert as its this context. You need to pass that along to the original function.

Number.prototype.toString() can take an optional radix argument. You should pass that along as well.

You can call a function with a specific this context and arguments by using Function.prototype.apply.

You also need to return the value returned by the original function.

(function() {
  let _toString = Number.prototype.toString;
  Number.prototype.toString = function(...args) {
    console.log("Number ToString Called");
    return _toString.apply(this, args);
  };
})();

let b = new Number(20);
console.log(b);
document.writeln(typeof b);
document.writeln(b.toString());
document.writeln(b.toString(8));