JavaScript using regex for validation

Question

I am validating a form and the text put into a form must be CIT, BIS or MATH

if(dept == ""){
     msg += "You must enter a department\n";
}else if((dept != "CIT") && (dept != "BIS") && (dept != "MATH")){
     msg += '"' + dept + '"' + " is not one of CIT, BIS, or MATH.\n";
}

I need to add some form of regex to make sure that the text CIT, BIS or MATH when input can be put in any form uppercase and lowercase.

Any help would be great Thanks

There is no need to use a regex here.

jahroy
– jahroy

2012-11-27 02:00:49 +00:00
Commented Nov 27, 2012 at 2:00 — jahroy
– jahroy, Commented Nov 27, 2012 at 2:00

jahroy · Accepted Answer · 2012-11-27 04:59:10Z

3

There's no need for a regex.

Just convert your input to lowercase before validating it.

if (dept == "") {
    msg += "You must enter a department\n";
}
else if (isInvalid(dept)) {
    msg += '"' + dept + '"' + " is not one of CIT, BIS, or MATH.\n";
}

function isInvalid(u) {
  var s = u.toLowerCase();
  var validStrings = [ "cit", "bis", "math" ];
  for (var i = 0; i < validStrings.length; i++) {
      if (s === validStrings[i]) {
          return false;
      }
  }
  return true;
}

As @y_nk has pointed out, the following approach would be more efficient (if necessary):

function isValid(s) {
    var validationObject = { "cit" : true, "bis": true, "math": true };
    return validationObject[ s.toLowerCase() ] === true;
}

edited Nov 27, 2012 at 4:59

answered Nov 27, 2012 at 1:54

jahroy

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5 Comments

y_nk Over a year ago

Would be more straightforward with: function isValid(str) { return ({ "cit": true, "bis": true, "math": true })[str.toLowerCase()] === true; }

jahroy Over a year ago

@y_nk - I don't see any benefit to that approach. I would rather write self-documenting code that is easy to read.

y_nk Over a year ago

There's no for-loop, no need to loop two times if it matches the third value. Also the toLowerCase should belong to the validation function since it's the lowercasing is mandatory. For the inlining, i'm not very found of it... i only wrote it in a line because it's a comment.

jahroy Over a year ago

@y_nk - After re-reading, I'll agree that your approach is technically more efficient. However, I would still opt for the more straightforward, easy to read approach (unless there was a real reason to modify it). Especially for an array with 3 elements and code that is clearly intended to be run as validation (where it probably will not be executed multiple times in a loop).

Pierce McGeough Over a year ago

Its part of an assignment and i need to use regex at some point and there is the best point.

Ja͢ck · Accepted Answer · 2012-11-27 02:41:32Z

1

If you really think regular expressions are the way:

if (!/^(?:BIS|CIT|MATH)$/i.test(dept)) {
}

The expression had to be anchored, which is why you also see the non-capturing group in there.

A nicer approach is this:

if (['cit', 'bis', 'math'].indexOf(dept.toLowerCase()) == -1) {
}

Unfortunately, that only works from IE9 onwards due to Array.indexOf()

edited Nov 27, 2012 at 2:41

answered Nov 27, 2012 at 1:59

Ja͢ck

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Comments

OJay · Accepted Answer · 2012-11-27 01:58:39Z

0

Something like this

var regex = new RegExp("^CIT$|^BIS$|^MATH$", "i");

if(dept == ""){
     msg += "You must enter a department\n";
}else if(!regex.test(dept)){
     msg += '"' + dept + '"' + " is not one of CIT, BIS, or MATH.\n";
}

answered Nov 27, 2012 at 1:58

OJay

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