Hashtag in [] in regex Javascript -

i'm doing exercise on codeacademy.com, , stumbled on exercise doesn't make sense. gave out error when tried include hashtag in first[]. i'm not sure why.

//change regexp have message  var emailregexp = /[a-z0-9._%+-#]+@[a-z0-9.-]+\.[a-z]{2,4}/; console.log(emailregexp.test("michael.courcy@microsoft.com")?"good":"bad"); console.log(emailregexp.test("michael.courcy@gmail.com")?"good":"bad"); console.log(emailregexp.test("###mic###@microsoft.com")?"good":"bad"); 

output

error 

you need escape - before #, otherwise thinks giving range, example 0-9:

[a-z0-9._%+\-#] 

so like:

var emailregexp = /[a-z0-9._%+\-#]+@[a-z0-9.-]+\.[a-z]{2,4}/;