Return True if a string doesn't match regex javascript

Your second condition is wrong: you're checking for a string that doesnt contain letters (upper or lowercase). And you forgot the square brackets in the regex. You should check for a string containing at least one uppercase letter:

if ((this.toUpperCase() === this) && (this.match(/[A-Z]/)))

You can do something like this:

var str = this;
var R = function(regex) {
    return (str.match(regex) || []).length
};
var ratio = {
    upper: R(/[A-Z]/g),
    lower: R(/[a-z]/g),
    letters: R(/[A-Z]/gi),
    spaces: R(/\s/g),
    non_letters: R(/[^A-Z]/gi)
};

and then you can use some logic like:

// if only upper case letters
if (this.length == ratio.upper + ratio.spaces)
    // do something ..

Hope it helps.

I think Fabius' answer is what you are looking for, but I'd recommend a few changes to the logic as you may end up catching more than and not all that you want:

• THIS IS SHOUTING!!
• Y?
• is the above SHOUTING?
• Please use SSCCE.
• wHAT ABOUT THIS? IS THIS SHOUTING?

Here's what I'd recommend:

var resultsDiv = $('#results'),
    tests = [
      { string: 'THIS IS SHOUTING!!' },
      { string: 'Y?' },
      { string: 'is the above SHOUTING?' },
      { string: 'Please use SSCCE.' },
      { string: 'wHAT ABOUT THIS? IS THIS SHOUTING?' }
    ];

$.each( tests, function(i, test){
  var string = test.string,
      isShouting;
  
  // First, strip out non-alpha characters:
  string = string.replace(/[^a-z]/ig, '');
  
  var beforeLength = string.length;
  
  // Now remove all uppercase characters:
  string = string.replace(/[^A-Z]/g, '');
  
  var afterLength = string.length;
  
  // Now, compare the length of the before and after, with a threshold for short string.
  // Basically, if the before string is at least 4 characters long and more than half of
  // the string is uppercase, then flag it as "shouting".
  isShouting =
    ( beforeLength >= 4 && ( afterLength / beforeLength >= 0.50 ) );
  
  $('<div>')
    .text(test.string)
    .css('color', 'darkblue')
    .appendTo( resultsDiv );
  
  $('<div>')
    .text(isShouting ? "SHOUTING DETECTED!" : "quiet and controlled.")
    .css('margin-bottom', '15px')
    .css('color', isShouting ? 'red' : 'black')
    .appendTo( resultsDiv );
  
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="results">
</div>

You can fiddle around with the thresholds to find something that will match your expectations. 50% uppercase may be too strict. Just keep in mind that there will always be exceptions to any rule, so make sure that the consequences of "shouting" aren't too onerous.

Also note that I haven't done much to internationalize this example. I leave that as an exercise to the reader. The example above is enough to demonstrate the theory.

You're asking about the regex, but your initial example doesn't use it so it sounds like you're going to regex just to cover the mistakes in the first example.

You don't need regex to do what you're looking to do.

If the string is okay to hold non-letter characters but the letters need to be all uppercase, try

if (this.toLowerCase() !== this)

to support internationalization you might want

if (this.toLocaleLowerCase() !== this)

Some languages have different casing rules, as explained in the docs toLacleLowerCase() doc