Doesn't this reverse all your prologues?

it will put the prologues as the first statement in the result array. I use unshift here because there is no guarantee in the order of this function when it gets call.

Right, but if you have existing 3 prologues, they'll be reversed.

var x = [];
[1,2,3].forEach(e => x.unshift(e))

x will have [3, 2, 1].

This function should only be getting called when adding to the beginning of an empty array anyway, so just document that and add an assertion if that's your concern.

I see what you mean now. But there are the same and it will not matter right? also if the prologue is sprinkle around the body function, it will be aggregate to the top so that should be ok as well?

The function is not necessary call at the beginning of an empty array. Like below the target statements-array may not be empty

But prologues need to go at the beginning, so what situations will you have where you're adding prologues other than to the beginning of the array? Any time this function gets called after anything, that's probably a bad sign.

But there are the same and it will not matter right?

Apart from preserving what the user wrote the best we can, that's unfortunately not necessarily true. From the spec:

Implementations may define implementation specific meanings for ExpressionStatement productions which are not a Use Strict Directive and which occur in a Directive Prologue.

So you don't actually know what your engine will want to do for some prologues and whether they are order-dependent. For instance, there used to be uncertainty on whether the "use asm directive should be allowed to come before a "use strict". https://bugzilla.mozilla.org/show_bug.cgi?id=877908

*step
Also, you should probably modified the comment to mention that it needs to be called whenever we transform the statement list of a source file, namespace, or function-like body.