Question

When I use switch statement , none of the cases matches the ‘prefix’.
But if I replace switch statement with if-else, everything works.
Why?

Thank you

//UPDATED
//el is DIV element. For example el.id='mph_4';
var prefix = /^[a-z]+/.exec(id);
//------------- SWTICH -------------------------
switch (prefix) {
    case 'mph':
        return 1;
    case 'ph':
        return 2;
    case 'mh':
        return 3;
}
//---------------IF-ELSE------------------------
 if (prefix == 'mph') {
        return 1;
    }
    else if (prefix == 'ph') {
        return 2;
    }
    else if (prefix == 'mh') {
        return 3;
    }

Answer 1

RegExp.exec() returns an array. So prefix is actually array and not a string. If you are sure that exec returns a single string, you can change your switch statement as:

switch (prefix[0]) {
    case 'mph':
        return 1;
    case 'ph':
        return 2;
    case 'mh':
        return 3;
}