RegEx not testing all characters

    let s = "1X7T4VrCs23k4vv08D6yQ3S19G4rVP188M9ahuxB6j1tMGZs1m10ey7eUj62WV2exLT4C83zl7Q80M"; // place your input string here.
    let k = 28; // change this number if you want to rotate the array with any other value.

    let alphabets = 'abcdefghijklmnopqrstuvwxyz';
    let orgnl = alphabets.split("");
    let revArr = alphabets.split("");
    let popedElements = [], index = [], outputString = [], output;

    let inputString = s;
    let caseString = inputString.split("");
    let str = inputString.toLowerCase().split("");
    // let pos = Number.parseInt(rotation.value);

    // For Regular Expressions
    let regEx = /[^a-zA-Z]/g;
    let popIn = [ ], tempPopIn = [ ], nonWord = [ ];

    // Storing the original index of the non Word character in popIn array
    for( let i = 0; i < caseString.length; i++ ){
        if( regEx.test(caseString[i]) ){
            popIn.push(i);
        }
    }

    // Storing the non word character from the original array to nonWord array
    popIn.forEach( (j) => nonWord.push(caseString[j]) );

    // Removing the non word character from the original array
    for( let i = 0; i < str.length; i++ ){
        if( regEx.test(str[i]) ){

            tempPopIn.push(i);
            tempPopIn.forEach( (j) => { 
                str.splice(j, 1);
                tempPopIn.pop();
            });
        }
    }

    // Rotating the original array by specified position
    for( let i = 0; i < k; i++ ){
        let remove = revArr.shift();
        revArr.push(remove);
    }

    // Finding index of input string in orgnl array and store it in an index array
    str.forEach( (i) => index.push(orgnl.indexOf(i)) );

    // Find the string at specified index in the rotated array
    index.forEach( (i) => outputString.push(revArr[i]) );

    // Making string from array
    for( let i = 0; i < popIn.length; i++ ){
        outputString.splice(popIn[i], 0, nonWord[i]);
    }

    // Checking letter case
    for( let i = 0; i < caseString.length; i++ ){
        if( caseString[i] === caseString[i].toUpperCase() ){
            outputString[i] = outputString[i].toUpperCase();
        }        
    }

    // Print the value to the output field
    output = outputString.toString().split(",").join("");    
    console.log(output);