Detect repeating letter in an string in Javascript

Question

code for detecting repeating letter in a string.

var str=\"paraven4sr\";
var hasDuplicates = (/([a-zA-Z])\\1+$/).test(str)        
alert(\"repeating string \         


        

Answer 1

JSFIDDLE

var str="paraven4sr";
var hasDuplicates = (/([a-zA-Z]).*?\1/).test(str)        
alert("repeating string "+hasDuplicates);

The regular expression /([a-zA-Z])\1+$/ is looking for:

• ([a-zA-Z]]) - A letter which it captures in the first group; then
• \1+ - immediately following it one or more copies of that letter; then
• $ - the end of the string.

Changing it to /([a-zA-Z]).*?\1/ instead searches for:

• ([a-zA-Z]) - A letter which it captures in the first group; then
• .*? - zero or more characters (the ? denotes as few as possible); until
• \1 - it finds a repeat of the first matched character.

If you have a requirement that the second match must be at the end-of-the-string then you can add $ to the end of the regular expression but from your text description of what you wanted then this did not seem to be necessary.