Array.find vs Array.forEach in performance

I was wondering if anyone knows if Array.find will short circuit the loop when the first item is found.

Yes, it will. This is clear from the spec, which shows it bailing as soon as the callback has returned a truthy value. Step 6(d):

If testResult is true, return kValue.

(Separately, it would be odd to keep searching even though a result had been found. If there had been early spec language doing that, it would have been caught and corrected before being finalized, and/or challenged by the makers of JavaScript engines [and others] as being inefficient.)

As you can see the polyfill code in here, you can notice that find loops until if there is something matched item.

Here is the part of that;

// 6. Repeat, while k < len
      while (k < len) {
        // a. Let Pk be ! ToString(k).
        // b. Let kValue be ? Get(O, Pk).
        // c. Let testResult be ToBoolean(? Call(predicate, T, « kValue, k, O »)).
        // d. If testResult is true, return kValue.
        var kValue = o[k];
        if (predicate.call(thisArg, kValue, k, o)) {
          return kValue;
        }
        // e. Increase k by 1.
        k++;
      }

So, ∀ n ∈ [0, len - 1]: n <= len - 1