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Ilya Kantor 2019-08-04 11:29:15 +03:00
parent 61bc426051
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1-js/08-prototypes/04-prototype-methods/article.md
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@ -26,6 +26,7 @@ let rabbit = Object.create(animal);
*/!*
alert(rabbit.eats); // true
*!*
alert(Object.getPrototypeOf(rabbit) === animal); // get the prototype of rabbit
*/!*
@ -78,7 +79,7 @@ As of now we have all these ways at our disposal.
Why was `__proto__` replaced by the functions `getPrototypeOf/setPrototypeOf`? That's an interesting question, requiring us to understand why `__proto__` is bad. Read on to get the answer.
```warn header="Don't reset `[[Prototype]]` unless the speed doesn't matter"
```warn header="Don't change `[[Prototype]]` on existing objects if speed matters"
Technically, we can get/set `[[Prototype]]` at any time. But usually we only set it once at the object creation time, and then do not modify: `rabbit` inherits from `animal`, and that is not going to change.
And JavaScript engines are highly optimized to that. Changing a prototype "on-the-fly" with `Object.setPrototypeOf` or `obj.__proto__=` is a very slow operation, it breaks internal optimizations for object property access operations. So evade it unless you know what you're doing, or JavaScript speed totally doesn't matter for you.
@ -111,7 +112,7 @@ Here the consequences are not terrible. But in other cases, we may be assigning
What's worst -- usually developers do not think about such possibility at all. That makes such bugs hard to notice and even turn them into vulnerabilities, especially when JavaScript is used on server-side.
Unexpected things also may happen when accessing `toString` property -- that's a function by default, and other built-in properties.
Unexpected things also may happen when assigning to `toString` -- that's a function by default, and other built-in methods.
How to evade the problem?
@ -160,7 +161,7 @@ alert(obj); // Error (no toString)
...But that's usually fine for associative arrays.
Please note that most object-related methods are `Object.something(...)`, like `Object.keys(obj)` -- they are not in the prototype, so they will keep working on such objects:
Note that most object-related methods are `Object.something(...)`, like `Object.keys(obj)` -- they are not in the prototype, so they will keep working on such objects:
```js run