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Add section to setAttributes documentation about immutability of attributes #12811

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talldan merged 3 commits into from
Dec 19, 2018
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Add section to setAttributes documentation about immutability of attributes #12811

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66d918d
Add section to setAttributes documentation about immutability of attr…
talldan Dec 12, 2018
6625cfa
Simplify explanation of immutable attributes
talldan Dec 13, 2018
712a592
Fix typo and add link to redux's immutability docs
chrisvanpatten Dec 19, 2018
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17 changes: 17 additions & 0 deletions docs/designers-developers/developers/block-api/block-edit-save.md
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Expand Up @@ -80,6 +80,23 @@ edit( { attributes, setAttributes, className, isSelected } ) {
}
```

When calling `setAttributes`, it's important that attributes are not mutated in the process of updating them. This is considered bad practice, the core of Gutenberg has been written with the same philosophies as Redux and state is treated as immutable data. It can also cause bugs. Objects and arrays are passed as references in JavaScript, so mutating them can affect other bindings to those references, for example an attribute's default value.
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@chrisvanpatten chrisvanpatten Dec 12, 2018

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This makes a lot of sense to document but I think the lingo might be slightly over the head of many WP developers.

It's obviously good to introduce and use higher level terms so folks can learn and expand their skills, but maybe this can be expanded with some extra context, definitions, etc.?

(This could also link into @mkaz's work on a JS tutorial, so we could point someone to some additional background.)

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@talldan talldan Dec 13, 2018

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Thanks for the feedback @chrisvanpatten—I've simplified the text a bit, tried using a simpler vocabulary.


```js
// Good - here a new array is created from the old list attribute and a new list item:
const { list } = attributes;
const addListItem = ( newListItem ) => setAttributes( { list: [ ...list, newListItem ] } );

// Bad - here the list from the existing attributes is mutated to add the new list item:
const { list } = attributes;
const addListItem = ( newListItem ) => {
list.push( newListItem );
setAttributes( { list } );
};

```


## Save

The `save` function defines the way in which the different attributes should be combined into the final markup, which is then serialized by Gutenberg into `post_content`.
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