dataList.js

// define example vars
var dataList = document.getElementById('suggestions'),
	letters = 'abcdefghijklmnopqrstuvwxyz',
	choices = letters.split(''),
	doubled = [];

// doubled letters
for(var i in choices) {
	var s = choices[i] + choices[i]; 
	doubled.push(s);
}
choices = choices.concat(doubled);

// populate datalist HTML5 method
// loop and add permutations of letters as options
for(var i=0; i<choices.length; i++) {
	var option = document.createElement('option');
	option.value = choices[i];
	dataList.appendChild(option);
}