Why would an Object prototype method override String and Number prototype methods in JavaScript?

Question

Trying to define a hashCode method on Object.prototype as well as String.prototype and Number.prototype . I'm defining the prototype methods using:

Object.defineProperty(Object.prototype, 'hashCode', {
  value:function() {/*code*/},
  enumerable:false
});

String.prototype.hashCode = function() {/*code*/};
Number.prototype.hashCode = function() {/*code*/};

When I create a number or string with any of ( '' , new String() , 3 , new Number() ), and call hashCode on the instance, the Object.prototype.hashCode method always runs instead of String.prototype.hashCode or Number.prototype.hashCode .

What's wrong?

Answer 1

Make the property descriptor writable: true or it will be inherited as non-writable when writing that property on objects that inherit it. http://jsfiddle.net/5ox1a0f2 – squint

 Object.defineProperty(Object.prototype, 'hashCode', { value:function() {console.log('object')}, enumerable:false, writable:true }); String.prototype.hashCode = function() {console.log('string')}; Number.prototype.hashCode = function() {console.log('number')}; 4..hashCode() 

Answer 2

Mixing property definitions and property assignments can lead to this kind of problems.

It works if you also use property definition in String.prototype and Number.prototype :

 Object.defineProperty(Object.prototype, 'hashCode', { value: function() {console.log('object')}, enumerable: false }); Object.defineProperty(String.prototype, 'hashCode', { value: function() {console.log('string')}, enumerable: false }); Object.defineProperty(Number.prototype, 'hashCode', { value: function() {console.log('number')}, enumerable: false }); (4).hashCode(); // "number" ('').hashCode(); // "string" 

However, if you are only using property definitions because you don't want enumerability, but don't care about configurability nor writability, it may be more convenient to define the methods via assignment, and then redefine the enumerability:

 Object.prototype.hashCode = function() {console.log('object')}; String.prototype.hashCode = function() {console.log('string')}; Number.prototype.hashCode = function() {console.log('number')}; Object.defineProperty(Object.prototype, 'hashCode', {enumerable: false}); Object.defineProperty(String.prototype, 'hashCode', {enumerable: false}); Object.defineProperty(Number.prototype, 'hashCode', {enumerable: false}); (4).hashCode(); // "number" ('').hashCode(); // "string"