Simple Duck Punching Example in Vanilla JavaScript

simple-duck-punching.js

// Duck Punching in JavaScript

const sentence = 'The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?';

const legacyIndexOf = String.prototype.indexOf;

// Extending the indexOf functionality to return the last occurence of the searchValue
String.prototype.indexOf = function (searchValue, fromIndex, getLastIndexFlag = false) {
  if (!getLastIndexFlag) {
  	return legacyIndexOf.call(this, searchValue, fromIndex);
  } else {
  	return legacyIndexOf.call(this.split(' ').reverse().join(' '), searchValue, fromIndex);
  }	
}