javascript regular expression help

[bonecone]

I want to use replace() to change the last occurence of a word which isn't necessarily at the end of a line. For example, replace the last occurence of 'duck' with 'goose' in "duck duck duck goose" so that it becomes "duck duck goose goose".

[bonecone]

I managed to find an answer afterwards. I'm new with regular expressions so I don't have a clue how this works. But here it is:

str1.replace(/(.*)duck/i, "$1goose")