how to put some variables in case in switch in js code example

Example 1: js convert if/else statement to switch case

var gradeOut = 70;
var totalGrade = 80;

if (gradeOut >= 90)
    gradeOut+= "My letter grade is: A";
  else if (totalGrade < 90 && totalGrade >= 80)
    gradeOut+= "My letter grade is: B";
  else if (totalGrade < 80 && totalGrade >= 70)
    gradeOut+= "My letter grade is: C";
  else if (totalGrade < 70 && totalGrade >= 60)
    gradeOut+= "My letter grade is: D";
  else if (totalGrade < 60)
    gradeOut+= "My letter grade is: F";

//here's the same thing using switch(true). Requires var gradeOut (is currently at top of page
switch(true) {
case gradeOut<60:
    gradeOut= "My letter grade is: F";
    break;
case gradeOut<70:
    gradeOut= "My letter grade is: D";
    break;
case gradeOut<80:
    gradeOut="My letter grade is: C";
    break;
}

Example 2: how to use switch case in javascript

switch (expression) {
  case value1:
    //Statements executed when the
    //result of expression matches value1
    [break;]
  case value2:
    //Statements executed when the
    //result of expression matches value2
    [break;]
  ...
  case valueN:
    //Statements executed when the
    //result of expression matches valueN
    [break;]
  [default:
    //Statements executed when none of
    //the values match the value of the expression
    [break;]]
}