在TypeScript中使用private

Question

This is a request for opinion, let's call it an RFO I hope this is received well by the community as I very much would like the feedback and feel overall we could all use some more insight on this often ignored issue.

I have been a C# developer since C# came out (I transitioned in from ASP). I have a natural tendency to use public and private when I write code. It's about impossible to stop me from adding public to my methods and properties in TypeScript even with it being default.

I am somewhat new to TypeScript, or even serious JavaScript (2 years in on typescript).

As we all know, private is in fact not private in the transpiled code. Therefore, while private member access is helpful to Typescript developers working alone or in a team, the output JavaScript is polluted with extra variables.

One may have getters and beautiful design principles, but in the end, what you have is a wall of variables that perform the same action , or at the least, negate all of our efforts to protect code. We use the underscore _toLetOthersKnowOurIntent. Angular's Style Guide suggest we avoid using _ on private variables.

The question is then, if you are writing code in typescript that is to be consumed by one using JavaScript (a package of some sort) is it more harmful and confusing to use private properties. Is the use or private only good for working with other TypeScript developers. If you are developing a library, say an Angular component to be distributed via NPM should one just avoid private all together?

Answer 1

TypeScript types and visibility features don't affect JavaScript output.

Since TypeScript is the language of choice in Angular community, private members will generally be respected in a library that was written in TypeScript.

Angular style guide is opinionated and doesn't necessarily take all considerations into account. TypeScript visibility is reflected in generated documentation and IDE, but it is always beneficial to have extra way to designate that a member isn't public, eg during debugging or using compiled TypeScript code with JavaScript.

Angular code base itself contains a lot of _ underscored members, just because this is convenient, so official style guide clearly isn't considered impeccable. The only time you regret is when there's a need for destructuring:

const { foo, bar } = this; // nice
const { _baz: baz, _qux: qux } = this; // not so nice

Another concern is that not every IDE or editor has full support for Angular templates. Due to how AOT compilation works, it requires all members that are used in component template to be public. This won't affect JIT compilation, which is usually used for development. Making sure that private members won't be accidentally used in template becomes developer's responsibility. This is another problem that _ Hungarian notation solves.

If there's a chance that a user can benefit from extending a class, consider using protected instead of private . There is no true encapsulation in JavaScript, so unsuitable visibility will never prevent a user from using third-party code the way a user wants but will just make jump through hoops.