How to assign a new value in switch case which in a function?

Question

Currently writing a function that converts a numerical grade into American system. Basically the result should be like this:

You got a D (60%)!

But I get this :

You got a 60 60%!

Apart from the brackets what should I do to make it look like as much as possible?

the code is below:

function gradeConverting(grade) {
    let gradePercent = grade + "%";
    switch (grade) {
        case (90 < grade && grade <= 100):
            grade = "A";
            break;
        case (80 < grade && grade <= 89):
            grade = "B";
            break;
        case (70 < grade && grade <= 79):
            grade = "C";
            break;
        case (60 <= grade && grade <= 69):
            grade = "D";
            break;
        case (50 <= grade && grade <= 59):
            grade = "E";
            break;
        case (grade <= 49):
            grade = "F";
            break;
    }
    return console.log("You got a " + grade + " " + gradePercent + "!");
}

gradeConverting(55);

Answer 1

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/switch

The MDN docs are one of the best resources for these types of Javascript syntax issues!

But essentially a switch statement in Javascript will only accept 1 expression followed but multiple outcomes of that expression.

Which within each specific case you can act on that outcome.

switch (value) {
    case 1:
        // do something for value == 1
        break;
    case 2:
        // do something for value == 1
        break;
    //...
}

Answer 2

You are not using using correctly the switch statement.

It is typically used with fixed values, like

switch (value) {
    case 1:
        // do something for value == 1
        break;
    case 2:
        // do something for value == 1
        break;
    //...
}

Additionally, you have no conversion for some values (90, 80 and 70) since you have strange bounds checks using inconsistently < and <=. (Change > to >= in the below code if you need to the lower tens included)

In your case, a sequence of if/else seems to be more appropriate:

function gradeConverting(grade) {
    let gradePercent = grade + "%";
    let americanGrade
    // note: you should probably specify what happens if grade > 100
    if (grade > 90) {
        americanGrade = "A";
    } else if (grade > 80) {
        americanGrade = "B";
    } else if (grade > 70) {
        americanGrade = "C";
    } else if (grade > 60) {
        americanGrade = "D";
    } else if (grade > 50) {
        americanGrade = "E";
    } else {
        americanGrade = "F";
    }
    return console.log("You got a " + americanGrade + " " + gradePercent + "!");
}

gradeConverting(55);

Note that you could shorten the code, for instance like this:

function toAmericanGrade(grade) {
    if (grade < 50) {
        return "F";
    } else if (grade >= 100) {
        return "A";
    }
    // `"F".charCodeAt(0) - 1 + 5` = `74`
    return String.fromCharCode(74 - Math.floor((grade)/10))
}

function gradeConverting(grade) {
    let gradePercent = `${grade}%`;
    let americanGrade = toAmericanGrade(grade)
    return console.log(`You got a ${americanGrade}${gradePercent}!`);
}

gradeConverting(55);

// test
for(let i = 45; i <= 100; i++) {
    gradeConverting(i);
}