如果满足某个条件，则退出程序

Question

如果没有学生姓名，或者输入的标记不在0到100之间，我希望程序退出：

var student = prompt("Please enter a student name [Press Cancel to exit]", "Cancel");

while(student !== null) {
    studentName.push(student);
    student = prompt("Please enter a student name [Press Cancel to exit]","Cancel");
}

function checkStudent() {
    for(var i = 0;i<studentName;i++) {
        if(studentName === null) {
          break;
        }
    }
    return document.write("We can't proceed if there is no student name");
}

checkStudent();

var mark = prompt("Please enter a mark[Press Cancel to exit]","Cancel");

while(mark!== null) {
    marks.push(mark);
    mark = prompt("Please enter a mark[Press Cancel to exit]", "Cancel");
}

function checkMark() {
    if(mark< 0 || 100<mark) {
        return
    }
}

checkMark()

document.write("Please enter a mark between 0 and 100")