Question

I have id’s validation method, each id can contain only [a-z0-9_] case insensitive characters. [^a-z] seems working, but I want to append [^0-9] but it’s not work. How one string pattern should looks like?

function foo() {
  testUserIds = ['id23425860', 
  'yulka_rdtska',
  'im?sel=2000000001',
  'im?sel=2000000002'];
  for (id in testUserIds) {
    document.write(isUserIdValid(id) + '\r\n');
  }
}
function isUserIdValid(user_id) {
  var patt = new RegExp('[^a-z]', 'ig');
  return patt.test(user_id);
}

Answer 1

The problem is that you are using a for-in construct instead of a proper for loop. Use [^a-z0-9_] as your regular expression and iterate correctly over your array.

In JavaScript, don’t iterate over arrays with for (elem in arr), as that syntax’s purpose is to iterate over properties of an object. Instead use for (var idx=0; idx<something; idx++).

function foo() {
  testUserIds = ['id23425860', 
  'yulka_rdtska',
  'im?sel=2000000001',
  'im?sel=2000000002'];

  // Use an incremental for loop here, NOT a for-in
  // for-in is intended for iterating over object properties, not arrays.
  for (var i=0; i<testUserIds.length; i++) {
    console.log(isUserIdValid(testUserIds[i]) + '\r\n');
  }
}
function isUserIdValid(user_id) {
  var patt = new RegExp('[^a-z0-9_]', 'ig');

  // Return the inversion of this, so isUserValid() is true if the user is valid
  return !patt.test(user_id);
}

foo();
// Outputs
true
true
false
false

Note that the way you have setup your function, it returns the opposite of what it says. You are checking for invalid characters, so return the inverted:

// If it matched, it's invalid, otherwise valid
return !patt.test(user_id);