regexp not working...arghhhh

I'm using Flex 4. I'm driving myself crazy. Why won't the following work?

//开发者_如何学运维 in my Application tag:

creationComplete="replaceMe(event)"

// in my script block:

public function replaceMe(event:Event):void{
var str:String = "She sells seashells by the seashore.";
var pattern:RegExp = /sh/gi;
str.replace(pattern, "sch");
test.text = str;
}

my text area (id="test") says "She sells seashells by the seashore."... it should say "sche sells seaschells by the seaschore."

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Because Strings are immutable objects. So, str.replace() just returns new string, without modifying str. Try

str = str.replace(pattern, "sch")

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Assign the new string value back to the old string like so:

str = str.replace(pattern, "sch");

Edit: Dzmitry answered first. =P