32 lines
1.2 KiB
Markdown
32 lines
1.2 KiB
Markdown
---
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title: nest
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tags: object,intermediate
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---
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Given a flat array of objects linked to one another, it will nest them recursively.
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Useful for nesting comments, such as the ones on reddit.com.
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- Use recursion.
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- Use `Array.prototype.filter()` to filter the items where the `id` matches the `link`, then `Array.prototype.map()` to map each one to a new object that has a `children` property which recursively nests the items based on which ones are children of the current item.
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- Omit the second argument, `id`, to default to `null` which indicates the object is not linked to another one (i.e. it is a top level object).
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- Omit the third argument, `link`, to use `'parent_id'` as the default property which links the object to another one by its `id`.
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```js
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const nest = (items, id = null, link = 'parent_id') =>
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items
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.filter(item => item[link] === id)
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.map(item => ({ ...item, children: nest(items, item.id, link) }));
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```
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```js
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// One top level comment
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const comments = [
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{ id: 1, parent_id: null },
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{ id: 2, parent_id: 1 },
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{ id: 3, parent_id: 1 },
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{ id: 4, parent_id: 2 },
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{ id: 5, parent_id: 4 }
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];
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const nestedComments = nest(comments); // [{ id: 1, parent_id: null, children: [...] }]
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```
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