Array.pop() vs Array.length=0

test.js

var arraySize = 10000

var a = []
var sumTime = 0

function setup () {
  for (var i = 0; i < arraySize; i+=1) {
    a.push(i)
  }
}

function cleanPop () {
  while(a.length > 0) {
    a.pop()
  }
}

function cleanLength () {
  a.length = 0
}

for (var i = 0; i < 10000; i+=1) {
  setup()
  var t1 = process.hrtime()
  // cleanPop()
  cleanLength()
  var diff = process.hrtime(t1)
  sumTime += (diff[0] * 1e9 + diff[1])
}

console.log(`took ${sumTime} nanosecs`)