javascript语法读者错了吗？

Question

i have this code , don't get me wrong it all work fine

var w = "window" ,
  gg = "gg" ,
  pr = "prototype" ,
  al = "alert" ,
  pi = "parseInt" ,
  st = String ,
  ts = "toString";

st[pr][gg] = function(){return window[this[ts]()];};
w = w[gg]();
w[al](w[pi]("0"));

the problem starts when i replace this piece of code

w = w[gg]();
w[al](w[pi]("0"));

with this one

w[gg]()[al](w[pi]("0"));

now it's not working.

i don't get it , it suppose to get the same result , what is wrong here?

Answer 1

There are two places that w is used:

w[al](w[pi]("0"));
^     ^

So you need to substitute in w[gg]() twice :

w[gg]()[al](w[gg]()[pi]("0"));
^^^^^^^     ^^^^^^^

Note also that this transformation might still not equivalent, for example if w[gg]() has side-effects or is non-deterministic.