// Returns true if the given character is an English vowel
function isVowel(char) {
	var vowels = ['a', 'e', 'i', 'o', 'u'];
	return vowels.indexOf(char.toLowerCase()) !== -1;
}

// Pig Latin algorithm
var words = ["peanut", "butter", "and", "jelly"];
for (var i = 0; i < words.length; i++) {
	var word = words[i];
	word += "-";
	var firstLetter = word.charAt(0);
	if (isVowel(firstLetter)) {
		word += "yay";
	} else {
		word += firstLetter;
		word += "ay";
		word = words.slice(1);
	}
	words[i] = word;
}

// Display magnificent result
console.log(words);