Question

I know that JavaScript doesn’t support private members, but you can emulate those. I’m wondering here is that if it’s worth it. Is there a point in making variables and/or functions private in JavaScript?

Answer 1

Is there a point in making variables and/or functions private in JavaScript?

I would argue ‘no’… and ‘no’ in more languages than merely JavaScript.

Information-hiding and encapsulation is all very commendable, but unless you have security boundaries inside your application, you don’t actually need to enforce privateness with strict language-level limits. Who is the untrusted attacker you’re protecting your code from? Yourself? Others in your team?

In a Java environment you might theoretically be writing a class to give limited access to a resource to a sandboxed party like an applet. In that case you wouldn’t want the applet code to be able to mess with private members as it might transgress over a security boundary.

But in JavaScript this isn’t possible. You get one security context per host:port and you can’t create effective security boundaries to limit code that shares your context. The ability to hide a variable is pretty meaningless when any JS code can completely take over the page’s UI. (Plus, some browsers have occasionally had features that defeat private variables, for example Mozilla’s old, now-removed __caller__.)

Consider instead the Python way: have a convention for effectively-private, even if the language doesn’t enforce it. Putting an underscore at the beginning of a member name is warning enough that class-users shouldn’t be messing with that member, but doesn’t make yourself a load of annoying extra work when you’re debugging or prototyping and need to temporarily ignore the privateness.