.match() with a regular expression returns null

Question

I am trying to do something I thought would be pretty easy to do, which is to restrict a string to certain characters by matching a regular expression.

var value = 'FailureStr1ng'; var type = 'ALPHA'; var regex = null;  switch(type) {     case 'ALPHA':         regex = '^[a-zA-Z]+$';         break;     case 'NUMERIC':         regex = '^[0-9]+$';         break;     case 'ALPHANUMERIC':         regex = '^[a-zA-Z0-9]+$';         break; }  return value.match(regex); 

For some reason, when using the match it always returns null. Is there a way to fix this, or a better method to do this?

Note: The code here is a snippet of much larger code, and in turn the value and type variable are usually defined by another method.

Answer 1

You want RegExp.test, which tests a value for a match instead of retrieving the match. With your existing code, that would mean:

if(!new RegExp(regex).test(value)){     alert('Your string was invalid.'); } 

However, it would be preferable to use RegExp literals instead of strings, as they're much more efficient and clear, and less prone to error:

var value = 'FailureStr1ng'; var type = 'ALPHA'; var regex = null;  switch(type) {     case 'ALPHA':         regex = /^[a-zA-Z]+$/;         break;     case 'NUMERIC':         regex = /^[0-9]+$/;         break;     case 'ALPHANUMERIC':         regex = /^[a-zA-Z0-9]+$/;         break; }  if(!regex.test(value)) {     alert('Your string was invalid.'); } 

Even better, use a dictionary:

var expressions = {     ALPHA: /^[a-zA-Z]+$/,     NUMERIC: /^[0-9]+$/,     ALPHANUMERIC: /^[a-zA-Z0-9]+$/ };  if(!expressions[type].test(value)) {     alert('Your string was invalid.'); }