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Dev JavaScript Optimising

How to write modern JS

So you’re learning JavaScript (JS), cool. Putting all this effort in, you’ll want to be learning the modern usage of the language right? Time to get strict.

“use strict” is something I recently stumbled across, and it seems like a really important thing to be using. So much so that I’m a bit surprised it hasn’t been mentioned in the course I’m doing. As it turns out, JS is full of legacy thinking. In an effort to keep new versions of the language compatible with older versions, much of this legacy thinking was/is retained. Obviously this limits JavaScripts ability to overcome its past and improve as time goes on.

Evidently, in 2009 a decision was made to start to modernise JS with the release of ECMAScript 5 (ES5). This meant breaking compatibility with older version of JS if you decided that was what you wanted to do. This is where “use strict” comes in. To enable this “modernisation” you include “use strict” at the top of your JS files like this:

"use strict";
// code below this will be implemented the modern way
...

Since it’s been 10 years since that decision was made, all modern browsers now support ES5. So unless you need to support browsers before the dawn of IE10 then you should be turning strict mode on for all of your JS development.

This of course begs the question, why? Well, aside from staying current with the language, there are also a number of practical benefits:

  1. Modern JS throws errors on things that where previously ignored. This helps you write better, more secure code
  2. It can improve the performance of your code, sometime significantly. Sometimes the code itself is identical and you just get a free performance boost, nice!
  3. It prevents some syntax being use that future version of the language are likely to use. AKA it future proofs your code

So from here on in, I’m going to be using strict mode exclusively and only avoid it when a situation presents itself that I can’t.

As always MDN is a good source of information on both strict and sloppy mode. Now go forth and write strict code!