It depends on what you mean by ignore. Do you want it to compile down to nothing so that it only works in uncompiled code? If so, you can use one of the standard @define values:
goog.implements = function (ctor, interfaceCtor) {
if (!COMPILED) {
...
}
};
or alternately, only when goog.DEBUG is enabled:
goog.implements = function (ctor, interfaceCtor) {
if (goog.DEBUG) {
...
}
};
if these don't fit you can define your own.
Or do you mean something else entirely?