Javascript function 返回“未定义”

Question

I've written aa function which takes score as parameter and should return the letter grade. There are some conditions to be followed while writing the code. ie: return 'A' if 25 < score <= 30 return 'B' if 20 < score <= 25 and so on. So I wanted to do this by omitting a whole lot of if-else's . As I'm new to javascript this is all I could come up with:

// This function takes Nested arrays and a single number, 
// which checks its availability in 
// the inside array and then return the index of the array
function my_index(arr, score) {
    for (const [index, elem] of arr.entries()) {
        if (elem.includes(score)) {
            return index;
        }
        
    }
}

// function to get letter grade
function getGrade(score) {
    let grade;
    var gradeDict = {
        'A': [26, 27, 28, 29, 30],
        'B': [21, 22, 23, 24, 25],
        'C': [16, 17, 18, 19, 20],
        'D': [11, 12, 13, 14, 15],
        'E': [6, 7, 8, 9, 10],
        'F': [0, 1, 2, 3, 4, 5] 
    }
    var keys = Object.keys(gradeDict);
    var values = [Object.values(gradeDict)]
    grade = keys[my_index(values, score)]
        
    return grade;
}

The first function works fine. It returns the index of nested array. But the main function getGrade happens to return 'Undefined' . Can't think of a better solution than this to reduce a bunch of ugly if-elses.

var question = {
    '1st': 'Can anybody help me get this done?',
    '2nd': 'Is there any better way to do this?'
}

Answer 1

Is there a better way to write this?

I'd do:

function getLetterGrade(score) {
  return ['F', 'F', 'E', 'D', 'C', 'B', 'A'][Math.ceil(score / 5)];
}

( F occurs twice because more scores map to F than to other grades)

It may be a bit cryptic, but is easier to tune should the possible score ever change.

Answer 2

Remove the outer [] array of the Object.values . Object.values already returns values in array .

from

var values = [Object.values(gradeDict)];

to

var values = Object.values(gradeDict);

working example:

 function my_index(arr, score) { for (const [index, elem] of arr.entries()) { if (elem.includes(score)) { return index; } } } function getGrade(score) { let grade; var gradeDict = { A: [26, 27, 28, 29, 30], B: [21, 22, 23, 24, 25], C: [16, 17, 18, 19, 20], D: [11, 12, 13, 14, 15], E: [6, 7, 8, 9, 10], F: [0, 1, 2, 3, 4, 5], }; var keys = Object.keys(gradeDict); var values = Object.values(gradeDict); grade = keys[my_index(values, score)]; return grade; } console.log(getGrade(5)); console.log(getGrade(25));

Alternate solution

 function getGrade(score) { let grade; var gradeDict = { A: [26, 27, 28, 29, 30], B: [21, 22, 23, 24, 25], C: [16, 17, 18, 19, 20], D: [11, 12, 13, 14, 15], E: [6, 7, 8, 9, 10], F: [0, 1, 2, 3, 4, 5], }; for (let key in gradeDict) { if (gradeDict[key].includes(score)) return key; } return "Not found"; } console.log(getGrade(5)); console.log(getGrade(25));

Answer 3

I like the ceil solution proposed earlier, but here is another general solution in case it's helpful:

function grade(score) {
  if (score < 0 || score > 30) throw RangeError(`Score ${score} out of range`);

  for (let ii = 5; ii >= 0; ii--) {
    if (score > 5*ii) return String.fromCharCode(70 - ii);
  }

  return 'F';
}

console.log(0, '=>', grade(0))   // F
console.log(4, '=>', grade(4))   // F
console.log(6, '=>', grade(6))   // E
console.log(10, '=>', grade(10)) // E
console.log(27, '=>', grade(27)) // A
console.log(30, '=>', grade(30)) // A