javascript - 从 html 输入中获取值

Question

我试图从 html 输入中获取值，但我无法使其正常工作，从我自己的研究来看，我的语法似乎正确？所以我很困惑。

当我控制台记录该值时，看起来它实际上并未获取输入的值。

let btn = document.getElementById("btn");
let grade = document.getElementById("gradeNum").value;

function getGrade() {
    console.log(grade);

    if (grade >= 90) {
        document.getElementById("gradeLetter").innerHTML = "You got an A!";
    } else if (grade < 90 && grade >= 80) {
        document.getElementById("gradeLetter").innerHTML = "You got a B!";
    } else if (grade < 80 && grade >= 70) {
        document.getElementById("gradeLetter").innerHTML = "You got a C!";
    } else if (grade < 70) {
        document.getElementById("gradeLetter").innerHTML = "You got an F! Study more!";
    }
};

Answer 1

试试这个:

let btn = document.getElementById("btn");
// let grade = document.getElementById("gradeNum").value; <-- NOT HERE

function getGrade() {
  let grade = document.getElementById("gradeNum").value;   // BUT HERE
  console.log(grade);

  if (grade >= 90) {
    ...