Why is const slower than var?

Question

I was testing performance differences between const and var in Javascript, when I noticed that const is slower than var.

I wrote a script to time const and var and compare them. It tests if const is faster 1000 times. const is faster only about 13% of the time.

function executionTime(code) {
  var t0 = performance.now()
  code()
  var t1 = performance.now()
  return t1 - t0
}

function test() {
    
  var results = [0, 0] // one, two - Which one is faster?
    
  for (var i = 0; i < 999; i++) {
    var one = executionTime(function() {
      const x = 'x'
    })

    var two = executionTime(function() {
      var x = 'x'
    })
        
    if (one > two) {
      results[0]++
    } else {
      results[1]++
    }
  }
    
  return ((results[0] < results[1]) ? 'Const is slower': 'Var is slower') + ' - const was faster ' + results[0] + ' times, and var was faster ' + results[1] + ' times'
}

console.log(test())

So, my question is, why is a variable declaration with var faster than one with const?

Answer 1

Once I ran a few tests with jsbench, as suggested in the comments, I realized that the performance could vary, and that my timing method was flawed.

JSBench: https://jsben.ch/eAiAk

So, there is no real time difference between const and var.