Javascript else if and getElementById issue

Hello

I found a problem in my quiz today to solve a problem in javascript about if-statment about calculating GPA , and I answer the question like this way I Found some issue to assign a value by name to integer .

var student = document.getElementById("student-name");
var math = document.getElementById("g1");
var mathcridit = document.getElementById("math-cridit");
var computer= document.getElementById("g2");
var compcridit=document.getElementById("compuetr-cridit");
var scie= document.getElementById("g3");
var scicridit=document.getElementById("sci-cridit");
var tot = document.getElementById("total");


math.addEventListener("input", grade);
mathcridit.addEventListener("input",calc)
computer.addEventListener("input",grade);
compcridit.addEventListener("input",calc);
scie.addEventListener("input",grade);
scicridit.addEventListener("input",calc);
function grade()
{
  if(document.getElementByIName('g')=='A')
    {
     return document.getElementByName('g')== 4;
    }
  else if (document.getElementByName('g')=='B')
    {
      return document.getElementByName('g')==3;
    }
  else if (document.getElementByName('g')=='C')
    {
      return document.getElementByName('g')==2;
    }
  else if (document.getElementByName('g')=='D')
    {
        return document.getElementByName('g')==1;
     
    }
 else  (document.getElementByName('g')=='F')
  {
    return 0;
  }
  
}
function calc() {
  var m = parseFloat([math.getElementByID("g1")].value);
  var c = parseFloat([computer.getElementById("g2")].value) ;
  var s = parseFloat([scie.getElementById("g3")].value);
   var mc = parseFloat(mathcridit.value) ;
  var cc = parseFloat(compcridit.value) ;
    var sc = parseFloat(scicridit.value) ;
    
  
 alert(tot.innerHTML = "your GPA is " + ((m*mc)+(c*cc)+(s*sc))/11);
}

<header>
</header>
<main>
  <h4>Enter the information:</h4>
  <p>
   Student Name: <input id="student-name" type="text">  E-mail Address: <input id="student-name" type="text"> <br>
    Mathmatics :<input name="g" id="g1" type="text"><br>
   Mathmatic cridit hours: <input id="math-cridit"><br>
    Computer :<input name="g" id="g2" type="text"><br>
    Computer cridit hours:<input id="computer-cridit"><br>
    Scince:<input name="g" id="g3" type="text"><br>
        Scince cridit hour :<input id="sci-cridit">
    <input id="total">