js switch判断成绩

switch (expression) {
  case value1:
    // 当 expression 等于 value1 时执行的代码
    break;
  case value2:
    // 当 expression 等于 value2 时执行的代码
    break;
  // 可以有任意数量的 case 语句
  default:
    // 当 expression 不等于任何 case 的值时执行的代码
}

function getGrade(score) {
  let grade;
  switch (true) {
    case score >= 90:
      grade = 'A';
      break;
    case score >= 80:
      grade = 'B';
      break;
    case score >= 70:
      grade = 'C';
      break;
    case score >= 60:
      grade = 'D';
      break;
    default:
      grade = 'F';
  }
  return grade;
}

console.log(getGrade(85)); // 输出: B

function getGrade(score) {
  let grade;
  switch (true) {
    case score >= 90:
      grade = 'A';
      // 忘记添加 break
    case score >= 80:
      grade = 'B'; // 这里会错误地执行
      break;
    // ...
  }
  return grade;
}

const gradeMap = {
  'A': score => score >= 90,
  'B': score => score >= 80,
  'C': score => score >= 70,
  'D': score => score >= 60,
  'F': () => true
};

function getGrade(score) {
  for (const [grade, condition] of Object.entries(gradeMap)) {
    if (condition(score)) {
      return grade;
    }
  }
}