As the name says, these missions require knowledge of javascript. But they are only limited to analyzing, these missions do not include javascript injection. Here are the links to all the solutions of javascript missions.
Javascript Mission 1: Idiot Test
Javascript Mission 2: Disable Javascript
Javascript Mission 3: Math time!
Javascript Mission 4: Var?
Javascript Mission 5: Escape!
Javascript Mission 6: go go away .js
Javascript Mission 7: JS Obfuscation. FTW!
Good luck!!!