SOURCE

'use strict'


var RandomCharacterAnimation = function(options) {

/**
 * @default value for each parameters
 *
 */

	var defaults = {
		d_element	: '',
		d_type		: 'char',
		d_min		: 10,
		d_max		: 100,
		d_kerning	: 10,
	}

	this.size;
	this.getLettersArray	= [];
	this.getLettersChanges	= [];
	this.kerningSize		= [];
	this.currentChange		= 0;
	this.char				= 'abcdefghijklmnopqrstuvwxyz0123456789!?*()@￡$%^&_-+=[]{}:;\'"\\|<>,./~`×';
	this.charArray 			= [];
	this.requestId;


	// Create options by extending defaults with the passed in arguments
	if (arguments[0] && typeof arguments[0] === "object") {
      this.options = _extendDefaults(defaults, arguments[0]);
	}

}

/**
  * @function _extendDefaults
  * @description set defaults parameters if undefined
  * @param source 		| get defaults parameters
  * @param properties | choose & set the defaults
  * @private
  *
  */

function _extendDefaults(source, properties) {
	var property;
	for (property in properties) {
		if (properties.hasOwnProperty(property)) {
			source[property] = properties[property];
		}
	}
	return source;
}


RandomCharacterAnimation.prototype = {

	// Private functions

	/**
	 * @function _random
	 * @description generate a random number
	 * @param minNb & maxNb 	| allows to generate the number between 20 and 50 for example
	 * @private
	 *
	 */

	_random: function(minNb, maxNb) {
		return Math.floor(Math.random() * (maxNb - minNb) + minNb);
	},

	/**
	 * @function _getElementSize
	 * @description get the length of the DOM element and push in an array
	 * @param minNb & maxNb 	| allows to generate the number between 20 and 50 for example
	 * @private
	 *
	 */

	_getElementSize: function() {
		var i, thisLetter;
		var element_selected = document.querySelector(this.options.d_element).textContent;

			for (i in element_selected) {
				thisLetter = element_selected[i];
				this.getLettersArray.push(thisLetter);
			}
			return this.getLettersArray;

	},

	/**
	 * @function _setStructure
	 * @description display a span for every letter that will allow the animation
	 * @private
	 *
	 */

	_setStructure: function() {
		var element = document.querySelector(this.options.d_element);
		element.innerHTML = '';

		var i, j, characterContainer, thisContainer, array, kerningSize;

		for (i in this.getLettersArray) {
			characterContainer = document.createElement('span');
			array = this.getLettersArray[i];

			// display a whitespace
			if (array === ' ') {
					characterContainer.innerHTML = ' ';
			}

			characterContainer.classList.add('randomCharacter');
			element.appendChild(characterContainer);

			var letter = document.createTextNode(array);

			// ? one mooore hack ?
			characterContainer.appendChild(letter);
			characterContainer.style.opacity = '0';
		}

	},

	/**
	 * @function _setKerning
	 * @description adapt the letter spacing
	 * @description very useful if you're not using a monospace font
	 * @description don't try to delete this function
	 * @description except if you want new eyes
	 * @private
	 *
	 */

	_setKerning: function() {

		var kerning = this.options.d_kerning;
		var elem = document.querySelector(this.options.d_element);

		var i, j, thisContainer, array, kerningSize;

		for (i = 0; i < this.getLettersArray.length; i++) {
			j = i + 1; //hack
			thisContainer = elem.querySelector('.randomCharacter:nth-child(' + j + ')');
			thisContainer.style.padding = '0' + (Math.sqrt(kerning) / thisContainer.offsetWidth) + 'px';
			kerningSize = thisContainer.offsetWidth;
			this.kerningSize.push(kerningSize);
			thisContainer.style.width = kerningSize + 'px';
		}
	},

	/**
	 * @function _convertStringToArray
	 * @description transform every string to an array
	 * @description useful if you want to use your own character to generate the animation
	 * @param charType 	| type of character
	 * @private
	 *
	 */

	_convertStringToArray: function(charType) {
		var i, thisChar;
		for (i = 0; i < this.char.length; i++) {
				thisChar = this.char[i];
				this.charArray.push(thisChar);
		}
	},

	/**
	 * @function _setChange
	 * @description set when each letter will change until the end of the animation
	 * @private
	 *
	 */

	_setChange: function() {
		var i, setChange;

		for (i in this.getLettersArray) {
				setChange = this._random(this.options.d_min, this.options.d_max);
				this.getLettersChanges.push(setChange);
		}
	},

	/**
	 * @function _generateRandomCharacter
	 * @description the core of the animation
	 * @description generate a new character randomly
	 * @descritpion everytime the function is called
	 * @param charType 	| type of character
	 * @private
	 *
	 */

	_generateRandomCharacter: function() {

		var charType = this.options.d_type;
		var elem = document.querySelector(this.options.d_element);

		this.currentChange++;

		var chooseRandomLetter = this._random(0, this.getLettersArray.length);
		var generateContent, setContent, getChar;
		var changesPlaces = elem.querySelector('.randomCharacter:nth-child(' + (chooseRandomLetter + 1) + ')');

		if (charType === 'int') {
				generateContent = this._random(0, 9);
		} else if (charType === 'char') {
				getChar = this._random(0, this.charArray.length);
				generateContent = this.charArray[getChar];
		} else {
				getChar = this._random(0, charType.length);
				generateContent = charType[getChar];
		}

		changesPlaces.innerHTML = generateContent;
		changesPlaces.style.opacity = '1';
		elem.style.opacity = '1'

	},

	/**
	 * @function _checkNbChanges
	 * @description check the current number of changes
	 * @descritpion everytime the function is called
	 * @description and display the original letter asap.
	 * @private
	 *
	 */

	_checkNbChanges: function() {
		var i, j, k, thisChar, setContent, thisContainer;
		var elem = document.querySelector(this.options.d_element);

		for (i = 0; i < this.getLettersArray.length; i++) {
			j = i + 1; //hack
			thisChar = this.getLettersChanges[i];
			thisContainer = elem.querySelector('.randomCharacter:nth-child(' + j + ')');
			setContent = this.getLettersArray[i];

			if (this.currentChange > thisChar) {
					thisContainer.innerHTML = setContent;
			}
		}
	},

	/**
	 * @function _loop
	 * @description requestAnimationFrame
	 * @private
	 *
	 */

	_loop: function() {

	var self = this;

	this.requestId = requestAnimationFrame(function() {
			self._loop();

			if (self.currentChange > self.options.d_max) {
					self.stop();
			}

		});

		self._generateRandomCharacter(self.options.d_type);
		self._checkNbChanges();

	},

	// Public functions

	/**
	 * @function restart
	 * @description allows to restart the animation.
	 * @description useful for hover or else
	 * @param key 	| allows a key to restart the animation
	 * @default 		| false
	 * @public
	 *
	 */

	restart: function() {
		this.currentChange = 0;
		this._setChange();
		this._loop();
	},

	/**
	 * @function start
	 * @description trigger the animation
	 * @public
	 *
	 */

	start: function() {

		this._getElementSize();
		this._setStructure();
		this._setKerning();
		this._setChange();
		this._convertStringToArray();

		this._loop();

	},

	/**
	 * @function stop
	 * @description stop the requestAnimaionFrame #notEnoughObvious ? ?
	 * @public
	 *
	 */

	stop: function() {
		window.cancelAnimationFrame(this.requestId);
	}

};


// Single Usage - If you define the animation only for one element
var title = new RandomCharacterAnimation({
	d_element 	: '.random',
	d_kerning 	: 8000,
});

title.start();

/**
 * @example
 * @description usage of the plugin with a list of element in the same level
 *
 */

// Multiple Usage - For example for list
var animations = [
	{
		d_element 	: '.item-link1',
		d_min 		: 25,
		d_max		: 50,
	},
	{
		d_element 	: '.item-link2',
		d_min 		: 25,
		d_max		: 50,
	},
	{
		d_element 	: '.item-link3',
		d_min 		: 25,
		d_max		: 50,
	},
	{
		d_element 	: '.item-link4',
		d_min 		: 25,
		d_max		: 50,
	},
	{
		d_element 	: '.item-link5',
		d_min 		: 25,
		d_max		: 50,
	}
]

var obj = [];

for (var optionsAnim in animations) {
	var random = new RandomCharacterAnimation(animations[optionsAnim]);
	random.start();
	obj.push(random);
}

/**
 * @function getIndexOfElementInParent
 * @param element 	| selected node element. best use is like is event.target.parentNode
 * because if you this function it means that most probably there are others same
 * element in the same level
 * @description this function get the index of the selected element
 * @public
 *
 */

function getIndexOfElementInParent(element){
	var parent = element.parentNode;
	for (var index = 0; index <= parent.children.length - 1; index++){
		if(parent.children[index] === element){
			return index;
		}
	}
};

/**
 * @function newEvent
 * @param selected_element_class 	| this is too obvious, and it's a string.
 * @param _event 					| event, for example 'mouseenter'
 * @description this function is just an example. Feel free to
 * create your own function
 * @public
 *
 */

function newEvent(selected_element_class, _event){
	var items = document.querySelectorAll(selected_element_class);
	for (var i = 0; i <= items.length - 1; i++){
		items.item(i).addEventListener(_event, function(event) {
			// call getIndexOfElementInParent
			var currentItemIndex = getIndexOfElementInParent(event.target.parentNode)
			obj[currentItemIndex].restart();
		}, false);
	}
};

newEvent('.item-link','mouseenter');

<div class="content">
  <h1 class="random">Umar Farooq.cbs</h1>
</div>
<div class="social">
  <ul id="social-list">
    <li class="list-item"><a class="item-link item-link1" href="#">item-link1</a></li>
    <li class="list-item"><a class="item-link item-link2" href="#">item-link2</a></li>
    <li class="list-item"><a class="item-link item-link3" href="#k">item-link3</a></li>
    <li class="list-item"><a class="item-link item-link4" href="#">item-link4</a></li>
    <li class="list-item"><a class="item-link item-link5" href="#">item-link5</a></li>
  </ul>
</div>

* {
  margin: 0;
  padding: 0;
}

html, body {
  overflow: hidden;
  font-family: sans-serif;
  font-weight: 100;
  background-color: #212121;
  width: 100%;
  height: 100%;
  text-rendering: optimizeLegibility;
}
html .content, body .content {
  text-align: center;
  position: relative;
  top: 50%;
  transform: translateY(-50%);
}
html .content .random, body .content .random {
  color: #eee;
  opacity: 0;
  display: inline-block;
  font-size: 1.5rem;
  text-transform: uppercase;
  font-weight: 100;
  cursor: pointer;
}
html .social, body .social {
  position: absolute;
  bottom:30%;
  left: 50%;
  transform: translateX(-50%);
  width: 600px;
  text-align: center;
}
html .list-item, body .list-item {
  display: inline-block;
  width: 110px;
  text-align: center;
}
html .list-item .item-link, body .list-item .item-link {
  font-size: 12px;
  text-decoration: none;
  color: #7F7F7F;
  transition: .3s ease-out all;
}
html .list-item .item-link:focus, body .list-item .item-link:focus {
  outline: none;
}
html .list-item .item-link:after, body .list-item .item-link:after {
  content: "";
  position: relative;
  width: 0;
  height: 1px;
  display: block;
  z-index: 100;
  background-color: cyan;
  transition: .3s ease-out all;
  left: 50%;
  top: 5px;
  transform: translateX(-50%);
}
html .list-item .item-link:hover, body .list-item .item-link:hover {
  color: #eee;
}
html .list-item .item-link:hover:after, body .list-item .item-link:hover:after {
  width: 50px;
}

.randomCharacter {
  display: inline-block;
  height: 10px;
}