Google Closure Compiler - 如何为变量创建一个Extern（变量名不能像在Eval中那样改变）

I am using Google Closure Compiler in "SIMPLE_OPTIMIZATIONS" mode. The JavaScript uses an "Eval" statement with the variable "_u" embedded in the string. When Google Closure Compiler obfuscates the code, the variable name is changed to "a" and I get an error that "_u" is not defined in the console. My understanding is that an Extern will solve this problem, but I'm not sure how to write it. Thoughts?I am using Google Closure Compiler in "SIMPLE_O