How to verify a string in Javascript using regular expression?

Question

I am pretty noob at JavaScript RegExp. I just need to verify whether a string is 4 characters long and contains only caps letters (AZ). Any help, highly appreciated.

Answer 1

Quick and dirty way, you can easily do it using:

^[A-Z][A-Z][A-Z][A-Z]$

Snippet

 <input id="text" /> <input type="button" onclick="return check();" value="Check" /> <script> function check() { var value = document.getElementById("text").value; if (/^[AZ][AZ][AZ][AZ]$/.test(value)) alert("Passes"); else alert("Failed"); } </script> 

Shorter Version

^[A-Z]{4}$

This uses the quantifiers {4} .

Answer 2

You could use a quantifier as well with a range from A to Z and start and end position of the line.

/^[A-Z]{4}$/

Explanation

• /^[AZ]{4}$/

  • ^ asserts position at start of the string

    Match a single character present in the list below

    [AZ]{4}

    {4} Quantifier — Matches exactly 4 times

    AZ a single character in the range between A (ASCII 65) and Z (ASCII 90) (case sensitive)

  • $ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)

Answer 3

You could use this:

/^[AZ]{4}$/.test('your_string')

Example:

var str = 'YEAH';
if(/^[A-Z]{4}$/.test(str)) {
    //true
}
else {
    //false
}