Callback

callback.js

Array.prototype.click = function(fn, thisArg) {
  const _self = thisArg || this;
  
  for (let i = 0; i < _self.length; i++) {
    fn.apply(thisArg, [_self[i], i, thisArg]);
    
    // Mutation.
    thisArg.values[i] = i;
  }
};

let values = ['Hello', 'World'];

values.click(function(value, index, ctx) {
  console.log(value, index);
}, this);

console.log(values, this.values);