Preparation code

 
<script>
  Benchmark.prototype.setup = function() {
    var MIN_PRECISION = -Math.pow(2, 53),
                MAX_PRECISION = -MIN_PRECISION,
                // idNum will ensure identifiers are unique.
                idNum = [ MIN_PRECISION ];
    
    var id = MIN_PRECISION;
    var x;
    var join = Function.prototype.call.bind(Array.prototype.join);
    
    function nextUniqueId() {
                idNum[0]++;
                for(var i = 0; idNum[i] >= MAX_PRECISION && i < idNum.length; i++) {
                        idNum[i] = MIN_PRECISION;
                        if (i < idNum.length) idNum[i + 1]++;
                        else {
                                // Reset and add a digit.
                                idNum = map(idNum, function() { return MIN_PRECISION; });
                                push(idNum, MIN_PRECISION);
                                break;
                        }
                }
                return '{' + join(idNum, ',') + '}';
        }
  };

  Benchmark.prototype.teardown = function() {
    id = null; idNum = null;
    x = null;
  };
</script>

Test runner

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x = id++;

x = nextUniqueId();

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