How to replace text ?

[niceusername]

Hi
I am not able to find a replace function so it will replace text from a given text or variables. Please provide some solutions.
Thanks

[UA]

Tools -> Replace String

[niceusername]

Thanks @UA, Also how can i use javascript functions with BAS variables? can you given an example ?
Thanks

[Fox]

@niceusername Here is an example of a substitution on js test replace.xml

[niceusername]

@Fox Thank you