I have an application that stores a large number of plain objects in an array. Using Object.freeze I can prevent Vue from making the items in the array reactive, but whenever I replace the array with a new frozen array, Vue tries to traverse all of the items anyway.

Since the array itself is reactive (as a property on its parent object), I believe the traversal is caused by the following in traverse():

if (isA) {
   i = val.length;
   while (i--) traverse(val[i], seen);
}

I've been able to fix the problem by adding this line:

if (!Object.isExtensible(val)) return

Immediately inside of:

if (isA || isO) {
    if (!Object.isExtensible(val)) return // Addition
    if (val.__ob__) {
      var depId = val.__ob__.dep.id;

 ...

Comparing JS profiles with/without that line gives a dramatic increase in speed for me. Since it's frozen, there won't be any getters in there anyway so why look? Instead of maintaining my own fork, I wanted to see if there was a reason this shouldn't be added into core.