JS Algorithms

Some basic JavaScript algorithms inspired by FreeCodeCamp.com
    function factorialize(number1){
        var count = number1;
        if(count===0){
            return 1;
        }
        else{
            for(var i=1;i<count;i++){
                number1=number1*i;
            }
            return number1;
        }
    }
    factorialize(5);
    function findLongestWord(stringVal){
    var arrayOfStrings = stringVal.split(" ");
    var longestString='';
    
    for(var i=0;i<arrayOfStrings.length; i++){
        if(longestString.length < arrayOfStrings[i].length){
            longestString= arrayOfStrings[i];
        }
    }
    console.log(longestString);
    }
    
    findLongestWord("The force is strong in this one");
    function reverseString(str){
        str= str.split("");
        str= str.reverse();
        str = str.join("");
        return str;
    }
    
    reverseString('Hello');
    //GOAL: Find the first missing letter in alphabet
    //YouTube.com/CodingTutorials360
    
    function fearNotLetter(str){
    var alphabet = "abcdefghijklmnopqrstuvwxyz";
    alphabet=alphabet.split("");
    
    for(var i=0; i<str.length;i++){
        if(str[i]!=alphabet[i]){
            console.log(alphabet[i]);
            return alphabet[i];
        }
    }
    
    //Does the second string char's all exist in the first word
    //YouTube.com/CodingTutorials360
    
    function containedWithin(arr){
    var word1 = arr[0].toLowerCase();
    var word2 = arr[1].toLowerCase();
    for(var i=0;i<word2.length;i++){
        var value = word1.indexOf(word2[i]);
        if(value===-1){
            console.log("False: " + word2[i]);
            return false;
        }
    }
    console.log("True: All leters contained within.")
    //GOAL: Does 1st world have all the letters needed to spell the second word
    //YouTube.com/CodingTutorials360
    
    function mutation(arr){
    var word1 = arr[0].toLowerCase();
    var word2 = arr[1].toLowerCase();
    
    for(var i=0;i<word2.length;i++){
        var indexVal = word1.indexOf(word2[i]);
        if(indexVal===-1){
            console.log(word2 + ': false');
            return false;
        }
    }
    //GOAL: Return DNA array Pair of string being passed in
    //YouTube.com/CodingTutorials360
    
    function pairElement(stringVal){
        var splitArray= stringVal.split('');
        var pairArray=[];
    
    for(var i=0;i<splitArray.length;i++){
        if(splitArray[i]=="G"){
            pairArray.push(['G', 'C']);
        }
        else if(splitArray[i]=="C"){
            pairArray.push(['C', 'G']);
        }