Testing for the fastest JS string checks

string-check-performance.js

var hrtime = process.hrtime;

function checkForProp (a) {
  return !!a.toLowerCase
}

function checkToStringEqual (a) {
  return a.toString() === a
}

function checkTypeof (a) {
  return typeof a === 'string'
}

function checkTypeofLoose (a) {
  return typeof a == 'string'
}

function checkStringEqual (a) {
  return '' + a === a
}

var tests = [checkTypeofLoose, checkForProp, checkToStringEqual, checkTypeof, checkStringEqual]
var testStr = 'string'
var count = 10000

tests.forEach((t) => {
  const start = hrtime()

  for (let i = 0; i < count; i++) {
    t(testStr)
  }

  const end = hrtime()

  console.log(t.name, (end[1] - start[1]) / 1000)
})

$ node --version
v8.9.4
$ node string-check-performance.js
checkTypeofLoose 304.529
checkForProp 385.314
checkToStringEqual 1748.515
checkTypeof 1677.513
checkStringEqual 282.735