Question

I have found the following expression which is intended to modify the id of a cloned html element e.g. change contactDetails[0] to contactDetails[1]:

var nel = 1;
var s = $(this).attr(attribute);
    s.replace(/([^\[]+)\[0\]/, "$1["+nel+"]");
    $(this).attr(attribute, s);

I am not terribly familiar with regex, but have tried to interpret it and with the help of The Regex Coach however I am still struggling. It appears that ([^\[]+) matches one or more characters which are not ‘[‘ and \[0\]/ matches [0]. The / in the middle I interpret as an ‘include both’, so I don’t understand why the author has even included the first expression.

I dont understand what the $1 in the replace string is and if I use the Regex Coach replace functionality if I simply use [0] as the search and 1 as the replace I get the correct result, however if I change the javascript to s.replace(/\[0\]/, "["+nel+"]"); the string s remains unchanged.

I would be grateful for any advice as to what the original author intended and help in finding a solution which will successfully replace the a number in square brackets anywhere within a search string.

Answer 1

Find

/           # Signifies the start of a regex expression like " for a string
([^\[]+)    # Capture the character that isn't [ 1 or more times into $1
\[0\]       # Find [0]
/           # Signifies the end of a regex expression

Replace

"$1["       # Insert the item captured above And [
+nel+       # New index
"]"         # Close with ]

To create an expression that captures any digit, you can replace the 0 with \d+ which will match a digit 1 or more times.

s.replace(/([^\[]+)\[\d+\]/, "$1["+nel+"]");