I have a Node.js project in which I use ES6 syntax on the server and non-ES6 syntax on the browser side. I have also tried using ES6 syntax on the browser, but then I experienced problems when I visited the website on iPhones, so I switched back to 'old javascript syntax'.
I can, from Bootstrap's code on Github, see that they use ES6 (const, arrow functions, etc.) in the code for Bootstrap v4.
Is it clever to avoid using ES6 syntax until all used browsers support it? I assume that there always will be a few browsers being used that do not support the new syntax, so why would anyone ever dare to move to the new syntax? I know that it will be very few, but since all the stuff that is possible with ES6 is also possible without ES6, I do not see how it can be worth using the new syntax for the cost of losing potential customers on my website.
Do there exist some scripts that can make sure all my visitors' browsers support ES6?