RegEx that will match the last occurrence of dot in a string

You do not need a regex for this. String.lastIndexOf will do.

var str = 'tro.lo.lo.lo.lo.lo.zip';var i = str.lastIndexOf('.');if (i != -1) {    str = str.substr(0, i) + "@2x" + str.substr(i);}

See it in action.

Update: A regex solution, just for the fun of it:

str = str.replace(/\.(?=[^.]*$)/, "@2x.");

Matches a literal dot and then asserts ((?=) is positive lookahead) that no other character up to the end of the string is a dot. The replacement should include the one dot that was matched, unless you want to remove it.

javascript jquery regex string

Just use special replacement pattern $1 in the replacement string:

console.log("tro.lo.lo.lo.lo.lo.png".replace(/\.([^.]+)$/, "@2x.$1"));// "tro.lo.lo.lo.lo.lo@2x.png"

Expand snippet