grades.js

function getGrades() {
    let getinfo = document.getElementById('grades').value;
    let grade = 0;
    let aver = 'grade average';
    let gNumber = 0;


for(i = 0; i <= getinfo.length; i++){
     grade += parseInt(getGrades[i]); {

    if(getinfo >= 90 && getinfo <= 100){
        grade = "A"
    document.getElementById('letter').innerHTML = "A";
    }

    else if(getinfo >= 80 && getinfo <= 89){
      grade = "B";
    document.getElementById('letter').innerHTML = "B";
    }

    else if(getinfo >= 70 && getinfo <= 79){
        grade = "C";
    document.getElementById('letter').innerHTML = "C";
    }

    else if(getinfo >= 60 && getinfo <= 69){
        grade = "D";
    document.getElementById('letter').innerHTML = "D";
    }

    else if(getinfo >= 0 && getinfo <= 59){
        grade = "E";
    document.getElementById('letter').innerHTML = "E";
    }
}

    aver = gNumber/grade;
    document.getElementById('average').innerHTML = aver + '    ';

}
}