Nit: `_` is a very valid identifier. (Consider Underscore/Lodash) On Wed, Sep 13, 2017, 09:32 Alex Kodat <alexko...@gmail.com> wrote:
> Also, FWIW, since we’re talking about nanoseconds of performance, here, I > think slightly better than: > > return this.#random || (this.#random = Math.random()); > > Is > > return (this.#random === undefined) ? this.#random = Math.random() : > this.#random; > > This is because in the former, the compiled code has to determine whether > this.#random is coercible into a Boolean. At the very least, it has to do > an "Is this an object and, if so, not undefined ==> true" test. From first > principles, the ternary expression is going to be more efficient. It simply > checks if the value at this.#random is the same as the global undefined > value and, if not, returns that value. No extra tests necessary. > > And at least with V8 theory == practice in this case (at least in all my > tests). And yes, we're talking nanosecond here. > > While this looks a bit like the null propagation operator would be > applicable, it's really not. > > Also FWIW, if you get tired of seeing/typing undefined, we add _ to the > global object which means the above can be written as: > > return (this.#random === _) ? this.#random = Math.random() : > this.#random; > > You might think that this would perform worse than the undefined but, in > fact, for V8 it's identical -- undefined and _ are both just properties of > the global object. I think this reads especially well in function calls > where you want an undefined placeholder > > fooey(_, "whatever"); > > Visually, _ just says undefined to me. > > ---- > Alex Kodat > > From: es-discuss [mailto:es-discuss-boun...@mozilla.org] On Behalf Of > Andrea Giammarchi > Sent: Wednesday, September 13, 2017 2:31 AM > To: Steve Fink <sph...@gmail.com> > Cc: es-discuss@mozilla.org > Subject: Re: Lazy evaluation > > > The properties already existed, so defineProperty shouldn't modify the > order IIUC > > well, nope. the property existed in the prototype, not in the object. > > anyway, I guess private properties, that are a possible solution, will be > transpiled through a WeakMap so that most likely anything discussed in here > won't make sense and the future code would look like the following > > ```js > class A { > #random; > get random() { > return this.#random || > (this.#random = Math.random()); > } > } > > > // transpiled > var A = function (wm) { > function A() { > wm.set(this, {random: void 0}); > } > Object.defineProperties( > A.prototype, > { > random: { > configurable: true, > get: function () { > return wm.get(this).random || > (wm.get(this).random = Math.random()); > } > } > } > ); > return A; > }(new WeakMap); > ``` > > > > _______________________________________________ > es-discuss mailing list > es-discuss@mozilla.org > https://mail.mozilla.org/listinfo/es-discuss >
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