A way to replace strings in javascript

I am looking for the best way to replace strings in javascript. Only problem, I need it replaced like this:

Here's my string: The brown fox jumps over the brown fence

I need javascript to find two words like this: The **brown** fox jumps over the **brown** fence

And I need to replace the string with what is in the middle of those words: fox jumps over the

I've been looking online but I cant find anything.

Any idea?