32 lines
941 B
Markdown
32 lines
941 B
Markdown
---
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title: Deep merge objects
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type: snippet
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language: javascript
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tags: [object,function]
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author: chalarangelo
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cover: coffee-drip
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dateModified: 2021-07-25T05:00:00-04:00
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---
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Deeply merges two objects, using a function to handle keys present in both.
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- Use `Object.keys()` to get the keys of both objects, create a `Set` from them and use the spread operator (`...`) to create an array of all the unique keys.
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- Use `Array.prototype.reduce()` to add each unique key to the object, using `fn` to combine the values of the two given objects.
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```js
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const deepMerge = (a, b, fn) =>
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[...new Set([...Object.keys(a), ...Object.keys(b)])].reduce(
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(acc, key) => ({ ...acc, [key]: fn(key, a[key], b[key]) }),
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{}
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);
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```
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```js
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deepMerge(
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{ a: true, b: { c: [1, 2, 3] } },
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{ a: false, b: { d: [1, 2, 3] } },
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(key, a, b) => (key === 'a' ? a && b : Object.assign({}, a, b))
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);
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// { a: false, b: { c: [ 1, 2, 3 ], d: [ 1, 2, 3 ] } }
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```
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