Setup cost: Micro-benchmark for https://twitter.com/thejameskyle/status/905403367949647874

bench-james.js

// Micro-benchmark to answer the question in https://twitter.com/thejameskyle/status/905403367949647874

if (typeof console === 'undefined') console = {log:print};

var closuresOriginal = (function() {
  const outer = a => {
    const inner = b => a + b;
    return inner(2);
  };

  return function closuresOriginal(a) {
    return outer(a);
  }
});

var closuresInitialTransform = (function() {
  const inner = (a, b) => a + b;
  const outer = a => inner(a, 2);

  return function closuresInitialTransform(a) {
    return outer(a);
  }
});

var closuresSymbolTransform = (function() {
  const _a = Symbol('a');
  const inner = b => inner[_a] + b;
  const outer = a => {
    inner[_a] = a;
    return inner(2);
  };

  return function closuresSymbolTransform(a) {
    return outer(a);
  }
});

var closuresBind = (function() {
  const inner = (a, b) => a + b;
  const outer = inner.bind(undefined, 2);

  return function closuresBind(a) {
    return outer(a);
  }
});

var TESTS = [
  closuresOriginal,
  closuresInitialTransform,
  closuresSymbolTransform,
  closuresBind
];
var a = 40;

var n = 2e7;

function test(fn) {
  var result;
  for (var i = 0; i < n; ++i) result = fn(a);
  return result;
}

for (var j = 0; j < TESTS.length; ++j) {
  test(TESTS[j]);
}

for (var j = 0; j < TESTS.length; ++j) {
  var startTime = Date.now();
  test(TESTS[j]);
  console.log(TESTS[j].name + ':', (Date.now() - startTime), 'ms.');
}

Results for the setup cost of these forms:

closuresOriginal: 670 ms.
closuresInitialTransform: 925 ms.
closuresSymbolTransform: 2206 ms.
closuresBind: 1223 ms.