JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="result"></ul>

JavaScript

var length = 100000,
    dates = [];

for(var i=0; i<length; i++){
    dates.push(new Date(953018441000 + (Math.random()*100000) )); //Thu Mar 14 2000 00:20:41 GMT-0700 (PDT)
}

//Fastest in Chrome
//concatenation
var start = new Date().getTime();
for(var i=0, len=dates.length; i<len; i++){
    var x = dates[i].getMonth() + 1 + "/" + dates[i].getDate() + "/" + dates[i].getFullYear();
}

$('#result').append('<li> Concat: ' + (new Date().getTime() - start) + '</li>');

//array join
var start = new Date().getTime();
for(var i=0; i<dates.length; i++){
    var x = [dates[i].getMonth() + 1, '/', dates[i].getDate(), '/', dates[i].getFullYear()].join('');
}

$('#result').append('<li> Array: ' + (new Date().getTime() - start) + '</li>');

//String.concat
var start = new Date().getTime();
for(var i=0; i<dates.length; i++){
    var x = String().concat(dates[i].getMonth() + 1, '/', dates[i].getDate(), '/', dates[i].getFullYear());
}

$('#result').append('<li> String().concat: ' + (new Date().getTime() - start) + '</li>');