How to create a custom function similar to string.split() to reverse a string

Question

I'm trying to write a function on which if we pass the string like we do for split, it returns a string which is reversed -

This is what I've tried -

var abc = "hello"
var result;
String.prototype.reverser = function(str){
  var temparr = str.split('').reverse().join('');
  return temparr;
}
result = abc.reverser();
console.log(result);

I'm expecting olleh but rather getting -

VM1179:4 Uncaught TypeError: Cannot read property 'split' of undefined at String.reverser (:4:19) at :7:14

Answer 1

You don't need a parameter str . The string is already binded to the method on prototype. Just use this to access the string.

 var abc = "hello" var result; String.prototype.reverser = function(){ return this.split('').reverse().join(''); } result = abc.reverser(); console.log(result); 

Note: You shouldn't directly add enumerable properties to prototype . Instead use Object.defineProperty()

 var abc = "hello"; Object.defineProperty(String.prototype,'reverser',{ value:function(){ return this.split('').reverse().join(''); } }) var result = abc.reverser(); console.log(result) 

Answer 2

When extending String.prototype with your reverser() function, the string with the new method on it can be accessed with this ; the way you have defined it expects an argument (str) , that isn't provided. See how this can be used to access the string in this working snip:

 var abc = "hello" var anotherStr = "what do you know?" var result; var anotherResult; String.prototype.reverser = function(){ var temparr = this.split('').reverse().join(''); return temparr; }; result = abc.reverser(); anotherResult = anotherStr.reverser(); console.log(result); console.log(anotherResult);