results.txt

> /p/google/v8/out.gn/x64.release/d8 test.js
testFuncExpr 1345 ms
testFuncDecl 347 ms

test.js

'use strict';

function testFuncExpr(arr){
  let result = 0;
  arr.forEach((c) => { if(c % 2) result++ });
  return result;
}

function testFuncDecl(arr){
  let result = 0;
  const fn = (c) => { if(c % 2) result++ };
  arr.forEach(fn);
  return result;
}

var ARRAYS = [
  [0,1,2,3,4,5],
  [0,2,2,3,4,5],
  [0,3,2,3,4,5],
  [0,4,2,3,4,5],
  [0,5,2,3,4,5],
  [0,6,2,3,4,5]
];

function run(i, isFuncExpr){
  let arr = ARRAYS[i % ARRAYS.length];
  if (isFuncExpr) return testFuncExpr(arr);
  else return testFuncDecl(arr);
}

function bench(isFuncExpr){
  const start = Date.now();
  let end = 0;
  for (let i = 0; i < 1e7; ++i) {
    run(i, isFuncExpr);
  }
  end = Date.now();
  print(isFuncExpr ? 'testFuncExpr' : 'testFuncDecl', end - start, 'ms');
}

// Warmup
run(0, true);
run(0, false);
run(1, true);
run(1, false);

// Bench
bench(true);
bench(false);