Question

I’ve been writing a javascript function which returns true if the value matches one of about 4 values (just 3 in the example below). The problem is, when I have just two values the function works correctly, but adding a third breaks the code.

I’m pretty new to javascript and I’m guessing there’s a much better way of doing this? I’ve tried searching but found nothing as of yet.

Any help is much appreciated.

function isValid(elem, helperMsg){

                var sn6 = /[sS][nN]6/;
                var sn5 = /[sS][nN]5/;
                var sn38 = /[sS][nN]38/;

                if(elem.value.match(sn6 || sn5 || sn38)){
                        //do stuff
                        return true;
                }else{

                        return false;
                }
            }

Edit:

Here’s my second attempt with an array:

    function isLocal(elem, helperMsg){
        var validPostcodes=new Array();
            validPostcodes[0]= /[wW][rR]12/;       
            validPostcodes[1]= /[cC][vV]35/;
            validPostcodes[2]= /[sS][nN]99/;
            validPostcodes[3]= /[sS][nN]6/;
            validPostcodes[4]= /[sS][nN]5/;
            validPostcodes[5]= /[sS][nN]38/;
            validPostcodes[6]= /[oO][xX]29/;
            validPostcodes[7]= /[oO][xX]28/;

        var i = 0;

        for (i = 0; i < validPostcodes.length; ++i) {
            if(elem.value.match(validPostcodes[i])){
                    // do stuff
                    return true;
            }else{
                    alert(helperMsg);
                    elem.focus();
                    return false;
            }
        }
    }

Answer 1

a || b || c

is an expression that evaluates to a boolean. That means that you’re running either match(true) or match(false). You must write it as:

match(a) || match(b) || match(c)

Another option would be to store them in an array and loop over it. That would mean if the number of patterns grew you wouldn’t have to change code other than the list of patterns. Another approach, though limited to this situation, might be to change the pattern to one that is equivalent to or-ing the three options together (untested, and I’m a bit rusty on regex):

elem.value.match(/[sSnN][6|5|38]/)

Array based example:

var patterns = [/../, /.../];
for (var i = 0; i < patterns.length; ++i) {
    if (elem.value.match(patterns[i])) { return true; }
}

In real code, I would probably format it like this:

function isValid(elem, helperMsg){
    var patterns = [/../, /.../],
        i = 0;
    for (i = 0; i < patterns.length; ++i) {
        if (elem.value.match(patterns[i])) {
            return true;
        }
    }
}

That’s just a habit though since JavaScript hoists variables to the top of their scope. It’s by no means required to declare the variables like that.