gistfile1.js

function B1() {
  var start = Date.now();
  while (...) { /* do N iterations of test body */
    /* body of the case goes here {{{ */
    function X() { return "hello"; }
    // Strictly speaking you can't have FunctionDeclaration as a Statement (see http://es5.github.io/#x12)
    // However most implementations support this for compatibility reasons.
    // V8 for example hoists all FunctionDeclarations to the top level, just like it does with variable
    // declarations. This means in this case X is *not* created again and again everytime the loop is entered.
    // Essentially this loop becomes empty.
    /* }}} */
  }
  var end = Date.now();
  /* N / (end - start) gives ops per ms result */
}
 
function B2() {
  var start = Date.now();
  while (...) { /* do N iterations of test body */
    /* body of the case goes here {{{ */
    var X = function () { return "hello"; }
    // Unlike in the case above V8 would create a new closure evey time function literal expression
    // is evaluated. Creating an illusion that FunctionDeclaration above is considerably slower.
    // While in fact we are just comparing a loop that does nothing with a loop that does something.
    // [V8 also could just eliminate allocation of X but does not do that at them moment]
    /* }}} */
  }
  var end = Date.now();
  /* N / (end - start) gives ops per ms result */
}