JavaScript regex issue for folders names-CodePudding

I'm trying to create a regex to allow alphanumeric strings with hyphens, underscores and spaces allowed. The string must start with a number or a letter and be a maximum total of 20.

Here is my code:

    var regex = /^[a-zA-Z0-9] ([a-zA-Z0-9_ -]){0,20}$/;
    var newName = "12345678901234567890233_pm";
    if (regex.test(newName)) {
        console.log('yes');
    }else{
        console.log('no');
    }

My code always returns yes. Is my regex wrong please?

Thanks.

CodePudding user response：

Your use of the quantifier in the first character class does not do what you seem to think it does - it’s actually not at all necessary in this context. Additionally, since the first character class accounts for 1 of the 20 maximum characters, reduce the maximum quantifier in the second character class to 19:

    var regex = /^[a-zA-Z0-9][a-zA-Z0-9_ -]{0,19}$/;
    var newName = "12345678901234567890233_pm";
    if (regex.test(newName)) {
        console.log('yes');
    }else{
        console.log('no');
    }