运行多个 else if 语句

Question

When I run this code, only the INVALID (over 100) and High Distinction works. Any number below 80 also shows High Distinction. What have I done wrong?

function calculateGrade() {
    var fvalue = Number(prompt('Please enter final score for unit. Enter a whole    number only'));

    document.write('The final score entered is ' + fvalue + '<br />');

    if (fvalue > 100) {
        document.write('INVALID');
    } else if (80 <= fvalue <= 100) {
        document.write('High Distinction');
    } else if (70 <= fvalue <= 79) {
        document.write('Distinction');
    } else if (60 <= fvalue <= 69) {
        document.write('Credit');
    } else if (50 <= fvalue <= 59) {
        document.write('Pass');
    } else if (0 <= fvalue <= 49) {
        document.write('Fail');
    } else if (fvalue < 0) {
        document.write('INVALID');
    }

}

calculateGrade()

Answer 1

Your comparison syntax is invalid. You need to check one boundary at a time:

if (80 <= fvalue && fvalue <= 100) {

Same for the others.

To take it a step further, you only need to check one boundary, because the higher end is excluded by the else :

if (fvalue > 100) {
    document.write('INVALID');
} else if (80 <= fvalue) {
    document.write('High Distinction');
} else if (70 <= fvalue) {
// ...

Answer 2

This isn't java. But you can surely try this.

else if ( (fvalue >= 80) && (fvalue<= 100)) { document.write('High Distinction');