Hello World

  // 23.1.3.33 Array.prototype.toReversed ( )
  CreateMethodProperty(Array.prototype, 'toReversed', function toReversed() {
     // 1. Let O be ? ToObject(this value).
     var O = ToObject(this);
     // 2. Let len be ? LengthOfArrayLike(O).
     var len = LengthOfArrayLike(O);
     // 3. Let A be ? ArrayCreate(len).
     var A = ArrayCreate(len);
     // 4. Let k be 0.
     var k = 0;
     // 5. Repeat, while k < len,
     while (k < len) {
         // a. Let from be ! ToString((len - k - 1)).
         var from = ToString(len - k - 1);
         // b. Let Pk be ! ToString((k)).
         var Pk = ToString(k);
         // c. Let fromValue be ? Get(O, from).
         var fromValue = Get(O, from);
         // d. Perform ! CreateDataPropertyOrThrow(A, Pk, fromValue).
         CreateDataPropertyOrThrow(A, Pk, fromValue);
         // e. Set k to k + 1.
         k = k + 1;
    }
    // 6. Return A.
    return A;
  });

You found the easter egg. Can you find the others?

Maybe built using Bazel?

https://bazel.build