在JavaScript中检查字符串是否相等

Question

我正在处理一个从html接收字符串并检查该字符串是否等于另一个字符串的脚本。

我有些刺痛。 我收到从a到f的成绩，有些成绩被认可，有些成绩没有。 问题出在DE和F。==运算符可能出问题了吗？ 注意：我试图在第二个if语句之前警告成绩，并确保我收到一个字符串值，所以以下代码中出现了问题。 码：

if (course1_grade) {
    if (course1_grade == "A") {
        course1_point = 4.0 * course1_credit;
    } else if (course1_grade == "A-") {
        course1_point = 3.67 * course1_credit;
    } else if (course1_grade == "B+") {
        course1_point = 3.33 * course1_credit;
    } else if (course1_grade == "B") {
        course1_point = 3.0 * course1_credit;
    } else if (course1_grade == "B-") {
        course1_point = 2.67 * course1_credit;
    } else if (course1_grade == "C+") {
        course1_point = 2.33 * course1_credit;
    } else if (course1_grade == "C") {
        course1_point = 2.0 * course1_credit;
    } else if ($course1_grade == "C-") {
        course1_point = 1.67 * course1_credit;
    } else if (course1_grade == "D+") {
        course1_point = 1.33 * course1_credit;
    } else if (course1_grade == "D") {
        course1_point = 1.0 * course1_credit;
    } else if (course1_grade == "F") {
        course1_point = 0.0 * course1_credit;
    }
} else {
    course1_point = 0.0;
}

Answer 1

由于未声明变量$course1_grade ，因此您的代码在尝试检查C-级时$course1_grade 。 此后没有任何代码运行。

您可以通过删除该美元符号来修复代码，也可以使用查找，这将更加紧凑：

var gradeLookup = {
    "A" : 4,
    "A-": 3.67,
    "B+": 3.33,
    "B" : 3,
    "B-": 2.67,
    "C+": 2.33,
    "C" : 2,
    "C-": 1.67,
    "D+": 1.33,
    "D" : 1
};

course1_grade = (course1_grade || "").trim().toUpperCase();
course1_point = (gradeLookup[course1_grade] || 0) * course1_credit;

您可以使用的另一种方法是switch语句：

function getFactor(grade) {
    switch ((grade || "").trim().toUpperCase()) {
        case "A" : return 4.0;
        case "A-": return 3.67;
        case "B+": return 3.33;
        case "B" : return 3;
        case "B-": return 2.67;
        case "C+": return 2.33;
        case "C" : return 2;
        case "C-": return 1.67;
        case "D+": return 1.33;
        case "D" : return 1;
        default  : return 0;
    }
}

course1_point = getFactor(course1_grade) * course1_credit;

Answer 2

JLRishe发现了错误，请参见他/她的答案，这是正确的答案。 因此，这现在是带有代码的注释（因此使其成为CW）。

对于它的价值，我将使用查找映射表或switch ，而不是漫长的if/else系列。

地图：

var factor = {
  "A":  4.0,
  "A-": 3.67,
  "B+": 3.33,
  "B":  3.0,
  "B-": 2.67,
  "C+": 2.33,
  "C":  2.0,
  "C-": 1.67,
  "D+": 1.33,
  "D":  1.0,
  "F":  0.0
};
course1_point = (factor[course1_grade.trim().toUpperCase()] || 0.0) * course1_credit;

 var factor = { "A": 4.0, "A-": 3.67, "B+": 3.33, "B": 3.0, "B-": 2.67, "C+": 2.33, "C": 2.0, "C-": 1.67, "D+": 1.33, "D": 1.0, "F": 0.0 }; var course1_credit = 100; function test(course1_grade) { var course1_point = (factor[course1_grade.trim().toUpperCase()] || 0.0) * course1_credit; snippet.log("grade = " + course1_grade + ", points = " + course1_point); } test("a"); test("a-"); test("b+"); test("b"); test("b-"); test("c+"); test("C"); test("C-"); test("D+"); test("D"); test("F"); 

 <!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 --> <script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script> 

switch ：

switch (course1_grade.trim().toUpperCase()) {
  case "A":
    course1_point = 4.0 * course1_credit;
    break;
  case "A-":
    course1_point = 3.67 * course1_credit;
    break;
  case "B+":
    course1_point = 3.33 * course1_credit;
    break;
  case "B":
    course1_point = 3.0 * course1_credit;
    break;
  case "B-":
    course1_point = 2.67 * course1_credit;
    break;
  case "C+":
    course1_point = 2.33 * course1_credit;
    break;
  case "C":
    course1_point = 2.0 * course1_credit;
    break;
  case "C-":
    course1_point = 1.67 * course1_credit;
    break;
  case "D+":
    course1_point = 1.33 * course1_credit;
    break;
  case "D":
    course1_point = 1.0 * course1_credit;
    break;
  case "F":
    course1_point = 0.0 * course1_credit;
    break;
  default:
    course1_point = 0.0;
}

 var course1_credit = 100; function test(course1_grade) { var course1_point; switch (course1_grade.trim().toUpperCase()) { case "A": course1_point = 4.0 * course1_credit; break; case "A-": course1_point = 3.67 * course1_credit; break; case "B+": course1_point = 3.33 * course1_credit; break; case "B": course1_point = 3.0 * course1_credit; break; case "B-": course1_point = 2.67 * course1_credit; break; case "C+": course1_point = 2.33 * course1_credit; break; case "C": course1_point = 2.0 * course1_credit; break; case "C-": course1_point = 1.67 * course1_credit; break; case "D+": course1_point = 1.33 * course1_credit; break; case "D": course1_point = 1.0 * course1_credit; break; case "F": course1_point = 0.0 * course1_credit; break; default: course1_point = 0.0; } snippet.log("grade = " + course1_grade + ", points = " + course1_point); } test("a"); test("a-"); test("b+"); test("b"); test("b-"); test("c+"); test("C"); test("C-"); test("D+"); test("D"); test("F"); 

 <!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 --> <script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>