Let me start with a story. Once upon a time I stumbled upon an excellent article by Philip Walton where he describes how expensive script evaluations could (and should!) be deferred until the browser is idle or they are actually needed. One of the examples that awakened my interest was creating an instance of the Intl.DateTimeFormat object, as I was using this great API quite often but never thought it can cause real performance problems. Turns out it can, especially if used inside loops. Apart from the technique described in Philip’s article, another solution is to simply reuse Intl.DateTimeFormat instances instead of creating them every time.