JavaScript – Make Custom Functions with Prototype

Posted on April 2, 2015 by

In the current article, I will show you how to build functions for built-in objects in JavaScript. The way I know is using a prototype. Thus, I will create functions, giving us the last n values of an array or returning a capitalization of our string. It is useful and may save you some time.

The functions come one by one. With some explanations.

string.Capitalize()

This one is just one line of code. The idea is to return the string with the first letter capitalized. The built-in function toUpperCase() does the whole work:

String.prototype.capitalize = function(){
	return this.charAt(0).toUpperCase() + this.slice(1);
}

String.prototype.capitalize = function(){

return this.charAt(0).toUpperCase() + this.slice(1);

}

string.isBlank()

Not a science fiction again. It is a boolean function, telling us whether we have spaces before or after the string. It could be optimized, by using two returns and thus avoiding the if/else, but as far as it works OK, I will leave it as it is:

String.prototype.isBlank = function(){
	var result = this.trim();
	if (result.length>0){
		result = false;
	} else {
		result = true;
	}
	return result
}

String.prototype.isBlank = function(){

var result = this.trim();

if (result.length>0){

result = false;

} else {

result = true;

}

return result

}

string.words()

This function returns a list of the string values, separated by one or more spaces. RegEx is used:

String.prototype.words = function(){

	return this.split(/[ ]{1,}/);
}

String.prototype.words = function(){

return this.split(/[ ]{1,}/);

}

string.format()

This is indeed a valuable function. It does something, that is granted in languages such as C#. Anyway, now we have it in JavaScript as well:

String.prototype.format = function(dict) {
  var result = this;

  if(typeof(dict) === "object") {
    Object.keys(dict).forEach(function(key) {
      result = result.replace("{" + key + "}", dict[key]);
    });
    return result;
  }

  var args = [];
  var n = arguments.length;
  var i = 0;

  for(i; i < n; i+=1) {
    args.push(arguments[i]);
  }

  args.forEach(function(arg) {
    result = result.replace("{}", arg);
  });

  return result;
}

String.prototype.format = function(dict) {

var result = this;

if(typeof(dict) === "object") {

Object.keys(dict).forEach(function(key) {

result = result.replace("{" + key + "}", dict[key]);

});

return result;

}

var args = [];

var n = arguments.length;

var i = 0;

for(i; i < n; i+=1) {

args.push(arguments[i]);

}

args.forEach(function(arg) {

result = result.replace("{}", arg);

});

return result;

}

array.head() and array.tail()

These two functions return the first or the last element of an array. Also available in C#, now in JS 🙂

Array.prototype.head = function(){
	return this[0];
}


Array.prototype.tail = function(){
	var mirror = this
	var result = mirror.shift();
	return this;
}

Array.prototype.head = function(){

return this[0];

}

Array.prototype.tail = function(){

var mirror = this

var result = mirror.shift();

return this;

}

array.range()

Ever dreamt to build an array of numbers with a small function? Now it is available in JS:

Array.prototype.range = function(iStart,iEnd){
	var newRange = [];

	for (var i = iStart; i <= iEnd; i++) {
		newRange.push(i);
	};
	return newRange
}

Array.prototype.range = function(iStart,iEnd){

var newRange = [];

for (var i = iStart; i <= iEnd; i++) {

newRange.push(i);

};

return newRange

}

array.sum()

Summing an array in JS is as easy as in Python now. Enjoy it:

Array.prototype.sum = function(myArray){
	var myResult = 0;

	var n = this.length;
	var i = 0;

	for(i; i < n; i+=1) {
		myResult += this[i];
	}

	return myResult;
}

Array.prototype.sum = function(myArray){

var myResult = 0;

var n = this.length;

var i = 0;

for(i; i < n; i+=1) {

myResult += this[i];

}

return myResult;

}

array.product()

Multiplication of an array is not an issue any more:

Array.prototype.sum = function(myArray){
	var myResult = 0;

	var n = this.length;
	var i = 0;

	for(i; i < n; i+=1) {
		myResult += this[i];
	}

	return myResult;
}

Array.prototype.sum = function(myArray){

var myResult = 0;

var n = this.length;

var i = 0;

for(i; i < n; i+=1) {

myResult += this[i];

}

return myResult;

}

array.compact()

This function simply clears away your array from all values, which are going to return false – e.g.[false, 0, ““,null,undefined, NaN]. The array myForbidden is not used, it stays there as a reminder:

Array.prototype.compact = function(myArray){
	var myResult = [];
	var myForbidden = [false, 0, "",null,undefined, NaN];
	var n = this.length;
	var i = 0;

	for(i; i

Array.prototype.compact = function(myArray){

var myResult = [];

var myForbidden = [false, 0, "",null,undefined, NaN];

var n = this.length;

var i = 0;

for(i; i

array.take() and array.drop():

Taking the first N or the last N values of an array has never been easier in JS:

Array.prototype.take = function(firstN){
	var myResult = [];
	var i = 0;

	for (i; i

Array.prototype.take = function(firstN){

var myResult = [];

var i = 0;

for (i; i

array.dedup()

Do you remember the set() in Python? Now we have something similar to it in JS:

Array.prototype.dedup = function(myArray){
	myResult = [];
	var n = this.length;
	var i = 0;
	
	for (i; i

Array.prototype.dedup = function(myArray){

myResult = [];

var n = this.length;

var i = 0;

for (i; i

array.sample()

Simply showing a random value from the array. Nothing more:

Array.prototype.sample = function(){
	var max = this.length-1;
	var min = 0;
	
	var myRandomPosition = Math.floor(Math.random()*(max-min+1)+min);
	return this[myRandomPosition];
}

Array.prototype.sample = function(){

var max = this.length-1;

var min = 0;

var myRandomPosition = Math.floor(Math.random()*(max-min+1)+min);

return this[myRandomPosition];

}

That’s all folks! The whole code is available in my GitHub repo here. Enjoy it!