for-in-loop-property-added.js

Array.prototype.decimalfy = function() {
  for (var i = 0; i < this.length; i++) {
    this[i] = this[i].toFixed(2);
  }
};

var digits = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

for (var index in digits) {
  console.log(digits[index]);
}

/**
 0
 1
 2
 3
 4
 5
 6
 7
 8
 9
 function() {
 for (let i = 0; i < this.length; i++) {
  this[i] = this[i].toFixed(2);
 }
 }
 */