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Prototype Chain Cycles (#25980)

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* Prototype Chain Cycles

* Fix error message
This commit is contained in:
Zach Zhao
2019-02-16 23:28:39 -05:00
committed by Manish Giri
parent 86caa14ead
commit f9ffbe305c
1 changed files with 18 additions and 0 deletions
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18
guide/english/javascript/prototypes/index.md
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@@ -61,6 +61,24 @@ console.log(obj2.c); // undefined
In above snippet, the statement `var obj2 = Object.create(obj1)` will create `obj2` object with prototype `obj1` object. In other words, `obj1` becomes the prototype of `obj2` instead of `Object.prototype` by default. As you can see, `b` is not a property of `obj2`, you can still access it via the prototype chain. For `c` property, however, you get `undefined` value because it can't be found in `obj1` and `Object.prototype`. In above snippet, the statement `var obj2 = Object.create(obj1)` will create `obj2` object with prototype `obj1` object. In other words, `obj1` becomes the prototype of `obj2` instead of `Object.prototype` by default. As you can see, `b` is not a property of `obj2`, you can still access it via the prototype chain. For `c` property, however, you get `undefined` value because it can't be found in `obj1` and `Object.prototype`.
#### Limitations
While setting the prototypes of objects, ensure that the prototype chain does not form a cycle.
```
let apple = {};
let pear = {};
let carrot = {};
Object.setPrototypeOf(apple, pear)
Object.setPrototypeOf(pear, carrot)
Object.setPrototypeOf(carrot, apple) // ERROR!
```
This wil cause the javascript engine to throw a `TypeError: Cyclic __proto__ value` error.
The reasoning behind this is that the engine does not know which object is more "senior" when passing through the chain.
### Classes ### Classes
In ES2016, we now get to use the `Class` keyword as well as the methods mentioned above to manipulate `prototype`. The JavaScript `Class` appeals to developers from OOP backgrounds, but it's essentially doing the same thing as above. In ES2016, we now get to use the `Class` keyword as well as the methods mentioned above to manipulate `prototype`. The JavaScript `Class` appeals to developers from OOP backgrounds, but it's essentially doing the same thing as above.