JSFiddle - React, Tailwind, and code Playground

JavaScript

var targetDate = +new Date + 1000;
var cycles1 = 0, cycles2 = 0, cycles3 = 0, cycles4 = 0;
while (+new Date < targetDate) {
    var a = {};
    a.some_prop = 5;
    cycles1++;
}
targetDate = +new Date + 1000;
while (+new Date < targetDate) {
    var a = {};
    a['some_prop'] = 5;
    cycles2++;
}
targetDate = +new Date + 1000;
while (+new Date < targetDate) {
    var a = {};
    a['some-prop'] = 5;
    cycles3++;
}
targetDate = +new Date + 1000;
while (+new Date < targetDate) {
    var a = {};
    a['2ome_prop'] = 5;
    cycles4++;
}

alert('Tested during 1 second for each:\n.some_prop: ' + cycles1 + '\n"some-prop: ' + cycles2 + '\n"some-prop: ' + cycles3 + '\n2ome_prop: ' + cycles4);