will read un-gzipped test data from https://github.com/pkg/json/tree/master/testdata; run as: deno run -A test-deno.js

test-deno.js

import { readJsonSync }
  from "https://deno.land/std/fs/mod.ts";

const repetitions = 100
const dir = './testdata'
for(const file of Deno.readDirSync(dir)) {
  const fileName = `${dir}/${file.name}`
  const bytes = Deno.statSync(fileName).size
  let i = 1, avg = 0
  for(; i <= repetitions; i++) {
    const t = Date.now()
    const parsed = readJsonSync(fileName)
    const duration = Date.now() - t
    avg += duration
  }
  avg /= i
  const mbs = '' + Math.round((bytes / 1e6) / (avg / 1000))
  const avgMs = '' + Math.round(avg)
  console.log(` ${file.name.padEnd(20, ' ')} --> ` +
    `${avgMs.padStart(4, '  ')} ms, ` +
    `${mbs.padStart(4, ' ')} MB/s`)
}