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Osvaldo Dias dos Santos 2021-08-14 21:31:15 +01:00
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1-js/07-object-properties/01-property-descriptors/article.md
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@ -19,7 +19,7 @@ We didn't see them yet, because generally they do not show up. When we create a
First, let's see how to get those flags. First, let's see how to get those flags.
The method [Object.getOwnPropertyDescriptor](mdn:js/Object/getOwnPropertyDescriptor) allows to query the *full* information about a property. The method [Object.getOwnPropertyDescriptor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getOwnPropertyDescriptor) allows to query the *full* information about a property.
The syntax is: The syntax is:
```js ```js
@ -54,7 +54,7 @@ alert( JSON.stringify(descriptor, null, 2 ) );
*/ */
``` ```
To change the flags, we can use [Object.defineProperty](mdn:js/Object/defineProperty). To change the flags, we can use [Object.defineProperty](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty).
The syntax is: The syntax is:
@ -274,7 +274,7 @@ We can change `writable: true` to `false` for a non-configurable property, thus
## Object.defineProperties ## Object.defineProperties
There's a method [Object.defineProperties(obj, descriptors)](mdn:js/Object/defineProperties) that allows to define many properties at once. There's a method [Object.defineProperties(obj, descriptors)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperties) that allows to define many properties at once.
The syntax is: The syntax is:
@ -300,7 +300,7 @@ So, we can set many properties at once.
## Object.getOwnPropertyDescriptors ## Object.getOwnPropertyDescriptors
To get all property descriptors at once, we can use the method [Object.getOwnPropertyDescriptors(obj)](mdn:js/Object/getOwnPropertyDescriptors). To get all property descriptors at once, we can use the method [Object.getOwnPropertyDescriptors(obj)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getOwnPropertyDescriptors).
Together with `Object.defineProperties` it can be used as a "flags-aware" way of cloning an object: Together with `Object.defineProperties` it can be used as a "flags-aware" way of cloning an object:
@ -326,24 +326,24 @@ Property descriptors work at the level of individual properties.
There are also methods that limit access to the *whole* object: There are also methods that limit access to the *whole* object:
[Object.preventExtensions(obj)](mdn:js/Object/preventExtensions) [Object.preventExtensions(obj)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/preventExtensions)
: Forbids the addition of new properties to the object. : Forbids the addition of new properties to the object.
[Object.seal(obj)](mdn:js/Object/seal) [Object.seal(obj)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/seal)
: Forbids adding/removing of properties. Sets `configurable: false` for all existing properties. : Forbids adding/removing of properties. Sets `configurable: false` for all existing properties.
[Object.freeze(obj)](mdn:js/Object/freeze) [Object.freeze(obj)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze)
: Forbids adding/removing/changing of properties. Sets `configurable: false, writable: false` for all existing properties. : Forbids adding/removing/changing of properties. Sets `configurable: false, writable: false` for all existing properties.
And also there are tests for them: And also there are tests for them:
[Object.isExtensible(obj)](mdn:js/Object/isExtensible) [Object.isExtensible(obj)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isExtensible)
: Returns `false` if adding properties is forbidden, otherwise `true`. : Returns `false` if adding properties is forbidden, otherwise `true`.
[Object.isSealed(obj)](mdn:js/Object/isSealed) [Object.isSealed(obj)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isSealed)
: Returns `true` if adding/removing properties is forbidden, and all existing properties have `configurable: false`. : Returns `true` if adding/removing properties is forbidden, and all existing properties have `configurable: false`.
[Object.isFrozen(obj)](mdn:js/Object/isFrozen) [Object.isFrozen(obj)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isFrozen)
: Returns `true` if adding/removing/changing properties is forbidden, and all current properties are `configurable: false, writable: false`. : Returns `true` if adding/removing/changing properties is forbidden, and all current properties are `configurable: false, writable: false`.
These methods are rarely used in practice. These methods are rarely used in practice.