What do you mean precisely? Normally you prevent code injection by not allowing user-supplied strings to be interpreted as JavaScript in the first place, not by

What do you mean precisely? Normally you prevent code injection by not allowing user-supplied strings to be interpreted as JavaScript in the first place, not by trying to catch all the possible ways in which one can construct a script doing something harmful. There aren't so many ways to inject a <script> tag or something equivalent into the page.