ben.js

function benchmark(repeats, fn) {
    'use strict';
    repeats = Math.min(repeats|0, 10);
    const args = Array.prototype.slice.call(arguments, 2);
    const timeStart = (window.performance || Date).now();
    window.empty = (function(){
        var last;
        for(var i = 0; i < repeats; i++) {
            last = fn.apply(null, args);
        }
        return last;
    }());
    return (window.performance || Date).now()-timeStart;
}

_arr = Array.from(Array(1000), (e,i)=>({[Math.random()]: {[Math.random()]: [Math.random()]}}));
arr = JSON.stringify(_arr);
r = 1000*100;
console.log('Simple JSON.parse, '+r+' iterations: '+benchmark(r, ()=>JSON.parse(arr))+'ms');
console.log('JSON.parse with copy, '+r+' iterations: '+benchmark(r, ()=>JSON.parse(arr, (k,v)=>{
   if (v && typeof v === 'object' && !Array.isArray(v)) {
     return Object.assign(Object.create(null), v);
   }
   return v;
}))+'ms');
console.log('JSON.parse with __proto__ change, '+r+' iterations: '+benchmark(r, ()=>JSON.parse(arr, (k,v)=>{
   if (v && typeof v === 'object' && !Array.isArray(v)) {
     v.__proto__ = null
   }
   return v;
}))+'ms');