Regex JS - 如何用“_”将空格替换为表达式到括号中

Question

如何将包含在括号内的表达式中包含的空格替换为w？

var str = "This is my text {an other text} and blabla {again again}...";

REGEX JS代码获取

"This is my text {an_other_text} and blabla {again_again}..."

感谢您的帮助