Javascript function with regex, letters and length [closed]

I need a function with 4 input parameters:

• regex
• minLength
• maxLength
• letters

And it should return a string with these conditions!

I can write the function with letters and regex and also a function with letters and length and also regex and length conditions. But the all of them! not. Can somebody help me?!

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I am going to write some testcases for a login page. For the username input field, I need to create strings manually. I am looking for a solution to automate this.