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Flow: Fix the example for width subtyping (#558)

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SZ-CHENG HUANG 2020-07-05 19:05:07 +08:00 committed by GitHub
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@ -144,7 +144,7 @@ See: [Optional properties](https://flow.org/en/docs/types/primitives/#toc-option
## Objects ## Objects
{: .-three-column} {: .-three-column}
### Extra object fields ### Width subtyping
```js ```js
type Artist = { type Artist = {
@ -156,14 +156,13 @@ type Artist = {
```js ```js
const a: Artist = { const a: Artist = {
name: 'Miguel Migs', name: 'Miguel Migs',
label: 'Naked Music' label: 'Naked Music',
genre: 'House' // ✓ OK
} }
a.genre = 'House' // ✓ OK
``` ```
{: data-line="6"} {: data-line="6"}
You can add more fields to an object. A type with more properties is "wider" and is a subtype of a "narrower" type.
See: [Width subtyping](https://flow.org/en/docs/lang/width-subtyping/) See: [Width subtyping](https://flow.org/en/docs/lang/width-subtyping/)
@ -178,10 +177,13 @@ type Artist = {|
{: data-line="1,4"} {: data-line="1,4"}
```js ```js
const a: Artist = { ··· } const a: Artist = {
a.genre = 'House' // ✗ Error name: 'Miguel Migs',
label: 'Naked Music',
genre: 'House' // ✗ Error
}
``` ```
{: data-line="2"} {: data-line="4"}
Exact object types prevent extra properties from being added to an object. Exact object types prevent extra properties from being added to an object.